Andre Przywara
2013-Sep-03 15:53 UTC
[PROPOSAL] ARM/FDT: passing multiple binaries to a kernel
Hi, a normal Linux kernel currently supports reading the start and end address of a single binary blob via the FDT''s /chosen node. This will be interpreted as the location of an initial RAM disk. The Xen hypervisor itself is a kernel, but needs up to _two_ binaries for proper operation: a Dom0 Linux kernel and it''s associated initrd. On x86 this is solved via the multiboot protocol used by the Grub bootloader, which supports to pass an arbitrary number of binary modules to any kernel. Since in the ARM world we have the versatile device tree, we don''t need to implement the mulitboot protocol. So I''d like to propose a new binding which denotes binary modules a kernel can use at it''s own discretion. The need is triggered by the Xen hypervisor (which already uses a very similar scheme), but the approach is deliberately chosen to be as generic as possible to allow future uses (like passing firmware blobs for devices or the like). Credits for this go to Ian Campbell, who started something very similar [1] for the Xen hypervisor. The intention of this proposal is to make this generic and publicly documented. Looking forward to any comments! Thanks, Andre. [1] http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=docs/misc/arm/device-tree/booting.txt;h=94cd3f18a4e1317a35e1255bf5c6e1e091001d1a;hb=HEAD ---------------------------- * Multiple boot modules device tree bindings Boot loaders wanting to pass multiple additional binaries to a kernel shall add a node "module" for each binary blob under the /chosen node with the following properties: - compatible: compatible = "boot,module"; A bootloader may add names to more specifically describe the module, e.g. Xen may use "xen,dom0-kernel" or "xen,dom0-ramdisk". If possible a kernel should be able to use modules even without a descriptive naming, by enumerating them in order and using hard-coded meanings for each module (e.g. first is kernel, second is initrd). - reg: specifies the base physical address and size of a region in memory where the bootloader loaded the respective binary data to. - bootargs: An optional property describing arguments to use for this module. Could be a command line or configuration data. Example: /chosen { #size-cells = <0x1>; #address-cells = <0x1>; module@0 { compatible = "xen,linux-zimage", "xen,multiboot-module", "boot,module"; reg = <0x80000000 0x003dcff8>; bootargs = "console=hvc0 earlyprintk ro root=/dev/sda1 nosmp"; }; module@1 { compatible = "xen,linux-initrd", "xen,multiboot-module", "boot,module"; reg = <0x08000000 0x00123456>; }; ...
Rob Herring
2013-Sep-03 22:00 UTC
Re: [PROPOSAL] ARM/FDT: passing multiple binaries to a kernel
On Tue, Sep 3, 2013 at 10:53 AM, Andre Przywara <andre.przywara@linaro.org> wrote:> Hi, > > a normal Linux kernel currently supports reading the start and end address > of a single binary blob via the FDT''s /chosen node. > This will be interpreted as the location of an initial RAM disk. > > The Xen hypervisor itself is a kernel, but needs up to _two_ binaries for > proper operation: a Dom0 Linux kernel and it''s associated initrd. > On x86 this is solved via the multiboot protocol used by the Grub > bootloader, which supports to pass an arbitrary number of binary modules to > any kernel. > > Since in the ARM world we have the versatile device tree, we don''t need to > implement the mulitboot protocol.But surely there would be some advantage of reuse by using the multi-boot protocol since Xen, grub, and OS tools already support it for x86.> So I''d like to propose a new binding which denotes binary modules a kernel > can use at it''s own discretion. > The need is triggered by the Xen hypervisor (which already uses a very > similar scheme), but the approach is deliberately chosen to be as generic as > possible to allow future uses (like passing firmware blobs for devices or > the like). > Credits for this go to Ian Campbell, who started something very similar [1] > for the Xen hypervisor. The intention of this proposal is to make this > generic and publicly documented.Can you describe how you see the boot flow working starting with OS installer writes kernel, initrd, xen and ??? to disk. How does the bootloader know what to load? The OS may not have access to the dtb, so this has to be described to the bootloader as well.> > Looking forward to any comments! > > Thanks, > Andre. > > [1] > http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=docs/misc/arm/device-tree/booting.txt;h=94cd3f18a4e1317a35e1255bf5c6e1e091001d1a;hb=HEAD > ---------------------------- > * Multiple boot modules device tree bindings > > Boot loaders wanting to pass multiple additional binaries to a kernel shall > add a node "module" for each binary blob under the /chosen node with the > following properties: > > - compatible: > compatible = "boot,module"; > A bootloader may add names to more specifically describe the module, > e.g. Xen may use "xen,dom0-kernel" or "xen,dom0-ramdisk". > If possible a kernel should be able to use modules even without a > descriptive naming, by enumerating them in order and using hard-coded > meanings for each module (e.g. first is kernel, second is initrd). > > - reg: specifies the base physical address and size of a region in > memory where the bootloader loaded the respective binary data to. > > - bootargs: > An optional property describing arguments to use for this module. > Could be a command line or configuration data.> Example: > /chosen { > #size-cells = <0x1>; > #address-cells = <0x1>; > module@0 { > compatible = "xen,linux-zimage", "xen,multiboot-module", > "boot,module"; > reg = <0x80000000 0x003dcff8>; > bootargs = "console=hvc0 earlyprintk ro root=/dev/sda1 nosmp"; > }; > module@1 { > compatible = "xen,linux-initrd", "xen,multiboot-module", > "boot,module"; > reg = <0x08000000 0x00123456>; > };This has to be created and parsed typically in FDT format by early boot code, and I worry about the complexity this has. Being future proof and extensible is good, but we could meet today''s needs with something simple like this: bootargs = "xen args --- linux args"; xen,linux-image = <start size>; So, is having a more generic solution really needed? Rob
Andre Przywara
2013-Sep-04 08:43 UTC
Re: [PROPOSAL] ARM/FDT: passing multiple binaries to a kernel
On 09/04/2013 12:00 AM, Rob Herring wrote:> On Tue, Sep 3, 2013 at 10:53 AM, Andre PrzywaraHi Rob,>> a normal Linux kernel currently supports reading the start and end address >> of a single binary blob via the FDT''s /chosen node. >> This will be interpreted as the location of an initial RAM disk. >> >> The Xen hypervisor itself is a kernel, but needs up to _two_ binaries for >> proper operation: a Dom0 Linux kernel and it''s associated initrd. >> On x86 this is solved via the multiboot protocol used by the Grub >> bootloader, which supports to pass an arbitrary number of binary modules to >> any kernel. >> >> Since in the ARM world we have the versatile device tree, we don''t need to >> implement the mulitboot protocol. > > But surely there would be some advantage of reuse by using the > multi-boot protocol since Xen, grub, and OS tools already support it > for x86.Yes, but that is x86 only and multiboot is it''s nature quite architecture specific. The current(?) multiboot v2 spec has no official ARM support (only x86 and MIPS), so this would need to be "invented" first. While this is technically easy, ARM software currently has no support for multiboot at all: not in u-boot and not in Xen. Multiboot support in Xen lives entirely in the x86 directory, and big parts of it are even in assembly. I am about to write up a more elaborate technical rationale describing the problems with multiboot on ARM: https://wiki.linaro.org/AndrePrzywara/Multiboot>> So I''d like to propose a new binding which denotes binary modules a kernel >> can use at it''s own discretion. >> The need is triggered by the Xen hypervisor (which already uses a very >> similar scheme), but the approach is deliberately chosen to be as generic as >> possible to allow future uses (like passing firmware blobs for devices or >> the like). >> Credits for this go to Ian Campbell, who started something very similar [1] >> for the Xen hypervisor. The intention of this proposal is to make this >> generic and publicly documented. > > Can you describe how you see the boot flow working starting with OS > installer writes kernel, initrd, xen and ??? to disk. How does the > bootloader know what to load? The OS may not have access to the dtb, > so this has to be described to the bootloader as well.The idea is to use bootscripts (for instance in u-boot) to tackle this. See for an example below. I don''t see how the process would be differ significantly from the current process, where you have to load mostly two images, get hold of the DTB, enter image data into the DTB and launch the kernel. Now you just need to load an additional image and enter it''s properties into the DTB, actually in a pretty generic way.>> >> Looking forward to any comments! >> >> Thanks, >> Andre. >> >> [1] >> http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=docs/misc/arm/device-tree/booting.txt;h=94cd3f18a4e1317a35e1255bf5c6e1e091001d1a;hb=HEAD >> ---------------------------- >> * Multiple boot modules device tree bindings >> >> Boot loaders wanting to pass multiple additional binaries to a kernel shall >> add a node "module" for each binary blob under the /chosen node with the >> following properties: >> >> - compatible: >> compatible = "boot,module"; >> A bootloader may add names to more specifically describe the module, >> e.g. Xen may use "xen,dom0-kernel" or "xen,dom0-ramdisk". >> If possible a kernel should be able to use modules even without a >> descriptive naming, by enumerating them in order and using hard-coded >> meanings for each module (e.g. first is kernel, second is initrd). >> >> - reg: specifies the base physical address and size of a region in >> memory where the bootloader loaded the respective binary data to. >> >> - bootargs: >> An optional property describing arguments to use for this module. >> Could be a command line or configuration data. > >> Example: >> /chosen { >> #size-cells = <0x1>; >> #address-cells = <0x1>; >> module@0 { >> compatible = "xen,linux-zimage", "xen,multiboot-module", >> "boot,module"; >> reg = <0x80000000 0x003dcff8>; >> bootargs = "console=hvc0 earlyprintk ro root=/dev/sda1 nosmp"; >> }; >> module@1 { >> compatible = "xen,linux-initrd", "xen,multiboot-module", >> "boot,module"; >> reg = <0x08000000 0x00123456>; >> }; > > This has to be created and parsed typically in FDT format by early > boot code, and I worry about the complexity this has. Being future > proof and extensible is good, but we could meet today''s needs with > something simple like this:Parsing this is already done in Xen, for instance. In fact we just look for nodes matching "boot,module" and then check for other names to determine it''s type (which is a few-liner patch in Xen which I will post later today). And I don''t see a need to load modules that early that we don''t have an un-flattened tree available. Generating is also part of libfdt, in fact this whole subtree above has been generated on the command line of a stock Calxeda U-Boot: dom0kernel=fdt addr ${fdt_addr}; fdt resize; fdt mknod /chosen module@0; fdt set /chosen/module@0 compatible "xen,linux-zimage" "xen,multiboot-module" "boot,module"; fdt set /chosen/module@0 reg <${dom0_addr_r} 0x${filesize}>; fdt set /chosen/module@0 bootargs "console=hvc0 earlyprintk ro root=/dev/sda1 nosmp" With this you load the Dom0 kernel (via TFTP or ext2load) and do "run dom0kernel" and are done. I have also patches which add an u-boot command called "module" which automates this, but this is mostly syntactic sugar (though may be useful for future abstraction, for instance to support the x86 (or even ARM) "real" multiboot protocol).> bootargs = "xen args --- linux args"; > xen,linux-image = <start size>; > > So, is having a more generic solution really needed?Not necessarily needed, but useful, I think. As described above I don''t see any technical obstacles of doing it in a more generic way, so we could as well go ahead with this. On x86 from time to time the need for additional binaries pops up (early microcode loading, for instance), so why not be be prepared. Also this approach avoids hard-coding the Xen name into the bootloader, as said in the proposal the meaning could be derived from the order of the modules (as on x86), so a bootloader does not need to know anything about Xen at all. Regards, Andre.
Ian Campbell
2013-Sep-04 08:44 UTC
Re: [PROPOSAL] ARM/FDT: passing multiple binaries to a kernel
On Tue, 2013-09-03 at 17:00 -0500, Rob Herring wrote:> On Tue, Sep 3, 2013 at 10:53 AM, Andre Przywara > <andre.przywara@linaro.org> wrote: > > Hi, > > > > a normal Linux kernel currently supports reading the start and end address > > of a single binary blob via the FDT''s /chosen node. > > This will be interpreted as the location of an initial RAM disk. > > > > The Xen hypervisor itself is a kernel, but needs up to _two_ binaries for > > proper operation: a Dom0 Linux kernel and it''s associated initrd. > > On x86 this is solved via the multiboot protocol used by the Grub > > bootloader, which supports to pass an arbitrary number of binary modules to > > any kernel. > > > > Since in the ARM world we have the versatile device tree, we don''t need to > > implement the mulitboot protocol. > > But surely there would be some advantage of reuse by using the > multi-boot protocol since Xen, grub, and OS tools already support it > for x86.Multiboot is pretty x86 specific (although MB2 has a MIPS port) and covers more stuff than we strictly require (e.g. on x86 it has requirements around which processor mode you enter in, has paging enabled etc).> > So I''d like to propose a new binding which denotes binary modules a kernel > > can use at it''s own discretion. > > The need is triggered by the Xen hypervisor (which already uses a very > > similar scheme), but the approach is deliberately chosen to be as generic as > > possible to allow future uses (like passing firmware blobs for devices or > > the like). > > Credits for this go to Ian Campbell, who started something very similar [1] > > for the Xen hypervisor. The intention of this proposal is to make this > > generic and publicly documented. > > Can you describe how you see the boot flow working starting with OS > installer writes kernel, initrd, xen and ??? to disk.Kernel and initrd are written to /boot in the usual way (probably from kernel.deb or whatever). Xen would also normally come from a distro package (also in /boot).> How does the bootloader know what to load?It''s in the bootloader config, e.g. boot.scr or grub.cfg, which are either hand written or produced by the distros tooling. grub on ARM could consume the same stanzas as are used by grub on x86 to boot Xen (which are produced by update-grub): echo ''Loading Xen 4.1-amd64 ...'' multiboot /xen-4.1-amd64.gz placeholder echo ''Loading Linux 3.10-2-amd64 ...'' module /vmlinuz-3.10-2-amd64 placeholder root=/dev/mapper/disks-root ro resume=/dev/mapper/disks-swap quiet echo ''Loading initial ramdisk ...'' module /initrd.img-3.10-2-amd64 Since there is no multiboot on ARM (and never will be) this is safe. If multiboot ever does come to ARM it will necessarily be multiboot2 which uses a different keyword. For u-boot Andre has proposed some syntactic sugar over the "fdt" command to make boot.scr more trivial to use. We would of course need to implement support for using it in the relevant distro tools (but they tend to be very distro/machine specific already, e.g. Debian''s flash-kernel)> The OS may not have access to the dtb, > so this has to be described to the bootloader as well.Right. The proposal is not for the OS to frob the DTB to support this protocol but to configure the bootloader to do it. Ian.
Ian Campbell
2013-Sep-04 08:55 UTC
Re: [PROPOSAL] ARM/FDT: passing multiple binaries to a kernel
On Wed, 2013-09-04 at 10:43 +0200, Andre Przywara wrote:> I am about to write up a more elaborate technical rationale describing > the problems with multiboot on ARM: > > https://wiki.linaro.org/AndrePrzywara/MultibootDoesn''t seem to exist? A search for "mulitboot" doesn''t seem to throw up the one you meant either.> > So, is having a more generic solution really needed? > > Not necessarily needed, but useful, I think. As described above I don''t > see any technical obstacles of doing it in a more generic way, so we > could as well go ahead with this. On x86 from time to time the need for > additional binaries pops up (early microcode loading, for instance), so > why not be be prepared.I agree. There have also been occasions where people doing disaggregation have wanted to start multiple initial domains, requiring additional modules at load time. I don''t think being generic and extensible is costing too much here. Ian.
Andre Przywara
2013-Sep-04 09:14 UTC
Re: [PROPOSAL] ARM/FDT: passing multiple binaries to a kernel
On 09/04/2013 10:55 AM, Ian Campbell wrote:> On Wed, 2013-09-04 at 10:43 +0200, Andre Przywara wrote: > >> I am about to write up a more elaborate technical rationale describing >> the problems with multiboot on ARM: >> >> https://wiki.linaro.org/AndrePrzywara/Multiboot > > Doesn''t seem to exist? A search for "mulitboot" doesn''t seem to throw up > the one you meant either.Try again now. As mentioned "I am about to write ..." ;-) Thanks, Andre.>>> So, is having a more generic solution really needed? >> >> Not necessarily needed, but useful, I think. As described above I don''t >> see any technical obstacles of doing it in a more generic way, so we >> could as well go ahead with this. On x86 from time to time the need for >> additional binaries pops up (early microcode loading, for instance), so >> why not be be prepared. > > I agree. There have also been occasions where people doing > disaggregation have wanted to start multiple initial domains, requiring > additional modules at load time. I don''t think being generic and > extensible is costing too much here. > > Ian. >
Rob Herring
2013-Sep-04 16:41 UTC
Re: [PROPOSAL] ARM/FDT: passing multiple binaries to a kernel
Adding Dennis for a distro perspective. On Wed, Sep 4, 2013 at 3:44 AM, Ian Campbell <Ian.Campbell@citrix.com> wrote:> On Tue, 2013-09-03 at 17:00 -0500, Rob Herring wrote: >> On Tue, Sep 3, 2013 at 10:53 AM, Andre Przywara >> <andre.przywara@linaro.org> wrote: >> > Hi, >> > >> > a normal Linux kernel currently supports reading the start and end address >> > of a single binary blob via the FDT''s /chosen node. >> > This will be interpreted as the location of an initial RAM disk. >> > >> > The Xen hypervisor itself is a kernel, but needs up to _two_ binaries for >> > proper operation: a Dom0 Linux kernel and it''s associated initrd. >> > On x86 this is solved via the multiboot protocol used by the Grub >> > bootloader, which supports to pass an arbitrary number of binary modules to >> > any kernel. >> > >> > Since in the ARM world we have the versatile device tree, we don''t need to >> > implement the mulitboot protocol. >> >> But surely there would be some advantage of reuse by using the >> multi-boot protocol since Xen, grub, and OS tools already support it >> for x86. > > Multiboot is pretty x86 specific (although MB2 has a MIPS port) and > covers more stuff than we strictly require (e.g. on x86 it has > requirements around which processor mode you enter in, has paging > enabled etc). > >> > So I''d like to propose a new binding which denotes binary modules a kernel >> > can use at it''s own discretion. >> > The need is triggered by the Xen hypervisor (which already uses a very >> > similar scheme), but the approach is deliberately chosen to be as generic as >> > possible to allow future uses (like passing firmware blobs for devices or >> > the like). >> > Credits for this go to Ian Campbell, who started something very similar [1] >> > for the Xen hypervisor. The intention of this proposal is to make this >> > generic and publicly documented. >> >> Can you describe how you see the boot flow working starting with OS >> installer writes kernel, initrd, xen and ??? to disk. > > Kernel and initrd are written to /boot in the usual way (probably from > kernel.deb or whatever). Xen would also normally come from a distro > package (also in /boot). > >> How does the bootloader know what to load? > > It''s in the bootloader config, e.g. boot.scr or grub.cfg, which are > either hand written or produced by the distros tooling. > > grub on ARM could consume the same stanzas as are used by grub on x86 to > boot Xen (which are produced by update-grub): > echo ''Loading Xen 4.1-amd64 ...'' > multiboot /xen-4.1-amd64.gz placeholder > echo ''Loading Linux 3.10-2-amd64 ...'' > module /vmlinuz-3.10-2-amd64 placeholder root=/dev/mapper/disks-root ro resume=/dev/mapper/disks-swap quiet > echo ''Loading initial ramdisk ...'' > module /initrd.img-3.10-2-amd64 > > Since there is no multiboot on ARM (and never will be) this is safe. > > If multiboot ever does come to ARM it will necessarily be multiboot2 > which uses a different keyword.Right, this is just a text file with a list of binaries. It is not really the multiboot spec. There is no reason for this part to be different for grub on ARM. There is a big advantage to reusing the distro side tooling. If there isn''t really much reuse on the bootloader side, then I''m fine with a different bootloader to Xen interface. I would like to hear that from folks working on grub though.> For u-boot Andre has proposed some syntactic sugar over the "fdt" > command to make boot.scr more trivial to use. We would of course need to > implement support for using it in the relevant distro tools (but they > tend to be very distro/machine specific already, e.g. Debian''s > flash-kernel)And being machine specific is a PITA. flash-kernel is certainly not something we want to expand on. There is not much love for boot.scr either. There is work to address what are not really machine differences, but largely vendor u-boot differences: http://www.mail-archive.com/u-boot@lists.denx.de/msg119025.html One option for u-boot which already supports syslinux style menu files is to adopt the syslinux multiboot parsing support: http://www.syslinux.org/wiki/index.php/Doc/mboot We need to back-up and consider what this looks like in the end for all the pieces and get input from folks on grub, UEFI, and armv8. The UEFI answer may be this is a grub problem. For armv8, this proposal does match up well as the kernel boot interface for v8 is DT. Despite some claims, ACPI will not completely replace DT because of this. Rob
Rob Herring
2013-Sep-05 13:23 UTC
Re: [PROPOSAL] ARM/FDT: passing multiple binaries to a kernel
On Wed, Sep 4, 2013 at 3:43 AM, Andre Przywara <andre.przywara@linaro.org> wrote:> On 09/04/2013 12:00 AM, Rob Herring wrote: >> >> On Tue, Sep 3, 2013 at 10:53 AM, Andre Przywara>> But surely there would be some advantage of reuse by using the >> multi-boot protocol since Xen, grub, and OS tools already support it >> for x86. > > > Yes, but that is x86 only and multiboot is it''s nature quite architecture > specific. The current(?) multiboot v2 spec has no official ARM support (only > x86 and MIPS), so this would need to be "invented" first. While this is > technically easy, ARM software currently has no support for multiboot at > all: not in u-boot and not in Xen. > Multiboot support in Xen lives entirely in the x86 directory, and big parts > of it are even in assembly.If so, I cannot find the assembly and most of it seems to be moved out of x86 code now. Rob
Andre Przywara
2013-Sep-06 13:30 UTC
Re: [PROPOSAL] ARM/FDT: passing multiple binaries to a kernel
On 09/05/2013 03:23 PM, Rob Herring wrote:> On Wed, Sep 4, 2013 at 3:43 AM, Andre Przywara > <andre.przywara@linaro.org> wrote: >> On 09/04/2013 12:00 AM, Rob Herring wrote: >>> >>> On Tue, Sep 3, 2013 at 10:53 AM, Andre Przywara > >>> But surely there would be some advantage of reuse by using the >>> multi-boot protocol since Xen, grub, and OS tools already support it >>> for x86. >> >> >> Yes, but that is x86 only and multiboot is it''s nature quite architecture >> specific. The current(?) multiboot v2 spec has no official ARM support (only >> x86 and MIPS), so this would need to be "invented" first. While this is >> technically easy, ARM software currently has no support for multiboot at >> all: not in u-boot and not in Xen. >> Multiboot support in Xen lives entirely in the x86 directory, and big parts >> of it are even in assembly. > > If so, I cannot find the assembly and most of it seems to be moved out > of x86 code now.There is some code that relocates and maps the multiboot structure: in files in the xen/arch/x86/boot directory, including head.S, reloc.c and setup.c. That would need to be completely rewritten, not only because it deals with multiboot v1, but also because it is scattered throughout the x86 setup code and the initial page setup is different from ARM. All these things are also done on ARM - but for the device tree already. Of course proper multiboot v2 support is doable - but please compare the effort needed for this against this one: http://lists.xen.org/archives/html/xen-devel/2013-09/msg00359.html Regards, Andre.
Grant Likely
2013-Sep-13 10:13 UTC
Re: [PROPOSAL] ARM/FDT: passing multiple binaries to a kernel
On Wed, Sep 4, 2013 at 5:41 PM, Rob Herring <robherring2@gmail.com> wrote:>> For u-boot Andre has proposed some syntactic sugar over the "fdt" >> command to make boot.scr more trivial to use. We would of course need to >> implement support for using it in the relevant distro tools (but they >> tend to be very distro/machine specific already, e.g. Debian''s >> flash-kernel) > > And being machine specific is a PITA. flash-kernel is certainly not > something we want to expand on. There is not much love for boot.scr > either. There is work to address what are not really machine > differences, but largely vendor u-boot differences: > > http://www.mail-archive.com/u-boot@lists.denx.de/msg119025.html > > One option for u-boot which already supports syslinux style menu files > is to adopt the syslinux multiboot parsing support: > > http://www.syslinux.org/wiki/index.php/Doc/mbootEven building it into U-Boot is problematic because it leaves older machines out in the cold. Leif''s port of Grub to U-Boot is far more interesting since the distro can now be in control of the code that loads the images and jumps into the kernel/hypervisor.> We need to back-up and consider what this looks like in the end for > all the pieces and get input from folks on grub, UEFI, and armv8. The > UEFI answer may be this is a grub problem. For armv8, this proposal > does match up well as the kernel boot interface for v8 is DT. Despite > some claims, ACPI will not completely replace DT because of this.Yes, for UEFI it is absolutely an OS loader problem. UEFI provides an API and runtime environment. Grub is in general moving towards a boot menu system and a tool for loading images. Actual booting however should be done by a separate OS loader application. For Linux, this will be an in-kernel UEFI Stub. For Xen I would recommend taking the Linux EFI stub code and doing the same thing. There really isn''t a need for a multiboot spec when you can rely on a runtime execution environment for setting things up exactly as you want them. Multiboot only makes sense to me when you need to rely on firmware or something else out of your control to load the images in a particular way. g.
Ian Campbell
2013-Sep-13 11:22 UTC
Re: [PROPOSAL] ARM/FDT: passing multiple binaries to a kernel
On Fri, 2013-09-13 at 11:13 +0100, Grant Likely wrote:> On Wed, Sep 4, 2013 at 5:41 PM, Rob Herring <robherring2@gmail.com> wrote: > >> For u-boot Andre has proposed some syntactic sugar over the "fdt" > >> command to make boot.scr more trivial to use. We would of course need to > >> implement support for using it in the relevant distro tools (but they > >> tend to be very distro/machine specific already, e.g. Debian''s > >> flash-kernel) > > > > And being machine specific is a PITA. flash-kernel is certainly not > > something we want to expand on. There is not much love for boot.scr > > either. There is work to address what are not really machine > > differences, but largely vendor u-boot differences: > > > > http://www.mail-archive.com/u-boot@lists.denx.de/msg119025.html > > > > One option for u-boot which already supports syslinux style menu files > > is to adopt the syslinux multiboot parsing support: > > > > http://www.syslinux.org/wiki/index.php/Doc/mboot > > Even building it into U-Boot is problematic because it leaves older > machines out in the cold. Leif''s port of Grub to U-Boot is far more > interesting since the distro can now be in control of the code that > loads the images and jumps into the kernel/hypervisor.AIUI this is not being developed any further?> > We need to back-up and consider what this looks like in the end for > > all the pieces and get input from folks on grub, UEFI, and armv8. The > > UEFI answer may be this is a grub problem. For armv8, this proposal > > does match up well as the kernel boot interface for v8 is DT. Despite > > some claims, ACPI will not completely replace DT because of this. > > Yes, for UEFI it is absolutely an OS loader problem. UEFI provides an > API and runtime environment. Grub is in general moving towards a boot > menu system and a tool for loading images. Actual booting however > should be done by a separate OS loader application. For Linux, this > will be an in-kernel UEFI Stub.I''m not sure I follow your distinction between loading the images and "actual booting". If grub loads the images and Linux stub does the actual booting how does this stub locate the images which grub loaded? Or are you saying the stub should load the initramfs itself? How does it know where to find it? Having the kernel in one config file (grub''s) and the initramfs in another (the Linux UEFI stub''s) seems likely to result in things getting out of sync. Having Linux''s stub parse the grub CFG is even less likely to work well IMHO.> For Xen I would recommend taking the > Linux EFI stub code and doing the same thing. There really isn''t a > need for a multiboot spec when you can rely on a runtime execution > environment for setting things up exactly as you want them.If this works for Linux on EFI then I see no reason it could work for Xen on EFI (assuming my questions above are just a result of my misunderstanding something) But... Xen also wants to support non-server and therefore non-EFI systems i.e. u-boot. We also want to support v7 where EFI is not a given even for servers AIUI. Given that I think it is a given that Xen will have some sort of protocol along these lines, for use in these environments even if it does the EFI stub thing on EFI systems. The question is shall we make it more general and useful to others or just go our own way? I''d prefer to do the former.> Multiboot only makes sense to me when you need to rely on firmware or > something else out of your control to load the images in a particular > way.I think in some cases do end up needing to rely on that though. Ian.
Rob Herring
2013-Sep-14 01:40 UTC
Re: [PROPOSAL] ARM/FDT: passing multiple binaries to a kernel
On Fri, Sep 13, 2013 at 5:13 AM, Grant Likely <grant.likely@secretlab.ca> wrote:> On Wed, Sep 4, 2013 at 5:41 PM, Rob Herring <robherring2@gmail.com> wrote: >>> For u-boot Andre has proposed some syntactic sugar over the "fdt" >>> command to make boot.scr more trivial to use. We would of course need to >>> implement support for using it in the relevant distro tools (but they >>> tend to be very distro/machine specific already, e.g. Debian''s >>> flash-kernel) >> >> And being machine specific is a PITA. flash-kernel is certainly not >> something we want to expand on. There is not much love for boot.scr >> either. There is work to address what are not really machine >> differences, but largely vendor u-boot differences: >> >> http://www.mail-archive.com/u-boot@lists.denx.de/msg119025.html >> >> One option for u-boot which already supports syslinux style menu files >> is to adopt the syslinux multiboot parsing support: >> >> http://www.syslinux.org/wiki/index.php/Doc/mboot > > Even building it into U-Boot is problematic because it leaves older > machines out in the cold. Leif''s port of Grub to U-Boot is far more > interesting since the distro can now be in control of the code that > loads the images and jumps into the kernel/hypervisor.Considering there is no distro support for grub on ARM yet, it may be more interesting in the long run, but it is not for the short term. So there needs to be something that is supportable on both u-boot and grub (or any other bootloader).> >> We need to back-up and consider what this looks like in the end for >> all the pieces and get input from folks on grub, UEFI, and armv8. The >> UEFI answer may be this is a grub problem. For armv8, this proposal >> does match up well as the kernel boot interface for v8 is DT. Despite >> some claims, ACPI will not completely replace DT because of this. > > Yes, for UEFI it is absolutely an OS loader problem. UEFI provides an > API and runtime environment. Grub is in general moving towards a boot > menu system and a tool for loading images. Actual booting however > should be done by a separate OS loader application. For Linux, this > will be an in-kernel UEFI Stub. For Xen I would recommend taking the > Linux EFI stub code and doing the same thing. There really isn''t a > need for a multiboot spec when you can rely on a runtime execution > environment for setting things up exactly as you want them.You''ve lost me as well. How do you see the flow working with UEFI for a user running bare metal OS, installing Xen, and rebooting running Xen. Rob
Dennis Gilmore
2013-Sep-14 04:06 UTC
Re: [PROPOSAL] ARM/FDT: passing multiple binaries to a kernel
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 El Wed, 4 Sep 2013 11:41:01 -0500 Rob Herring <robherring2@gmail.com> escribió:> Adding Dennis for a distro perspective. > > On Wed, Sep 4, 2013 at 3:44 AM, Ian Campbell > <Ian.Campbell@citrix.com> wrote: > > On Tue, 2013-09-03 at 17:00 -0500, Rob Herring wrote: > >> On Tue, Sep 3, 2013 at 10:53 AM, Andre Przywara > >> <andre.przywara@linaro.org> wrote: > >> > Hi, > >> > > >> > a normal Linux kernel currently supports reading the start and > >> > end address of a single binary blob via the FDT''s /chosen node. > >> > This will be interpreted as the location of an initial RAM disk. > >> > > >> > The Xen hypervisor itself is a kernel, but needs up to _two_ > >> > binaries for proper operation: a Dom0 Linux kernel and it''s > >> > associated initrd. On x86 this is solved via the multiboot > >> > protocol used by the Grub bootloader, which supports to pass an > >> > arbitrary number of binary modules to any kernel. > >> > > >> > Since in the ARM world we have the versatile device tree, we > >> > don''t need to implement the mulitboot protocol. > >> > >> But surely there would be some advantage of reuse by using the > >> multi-boot protocol since Xen, grub, and OS tools already support > >> it for x86. > > > > Multiboot is pretty x86 specific (although MB2 has a MIPS port) and > > covers more stuff than we strictly require (e.g. on x86 it has > > requirements around which processor mode you enter in, has paging > > enabled etc). > > > >> > So I''d like to propose a new binding which denotes binary > >> > modules a kernel can use at it''s own discretion. > >> > The need is triggered by the Xen hypervisor (which already uses > >> > a very similar scheme), but the approach is deliberately chosen > >> > to be as generic as possible to allow future uses (like passing > >> > firmware blobs for devices or the like). > >> > Credits for this go to Ian Campbell, who started something very > >> > similar [1] for the Xen hypervisor. The intention of this > >> > proposal is to make this generic and publicly documented. > >> > >> Can you describe how you see the boot flow working starting with OS > >> installer writes kernel, initrd, xen and ??? to disk. > > > > Kernel and initrd are written to /boot in the usual way (probably > > from kernel.deb or whatever). Xen would also normally come from a > > distro package (also in /boot). > > > >> How does the bootloader know what to load? > > > > It''s in the bootloader config, e.g. boot.scr or grub.cfg, which are > > either hand written or produced by the distros tooling. > > > > grub on ARM could consume the same stanzas as are used by grub on > > x86 to boot Xen (which are produced by update-grub): > > echo ''Loading Xen 4.1-amd64 ...'' > > multiboot /xen-4.1-amd64.gz placeholder > > echo ''Loading Linux 3.10-2-amd64 ...'' > > module /vmlinuz-3.10-2-amd64 placeholder > > root=/dev/mapper/disks-root ro resume=/dev/mapper/disks-swap quiet > > echo ''Loading initial ramdisk ...'' > > module /initrd.img-3.10-2-amd64 > > > > Since there is no multiboot on ARM (and never will be) this is safe. > > > > If multiboot ever does come to ARM it will necessarily be multiboot2 > > which uses a different keyword. > > Right, this is just a text file with a list of binaries. It is not > really the multiboot spec. There is no reason for this part to be > different for grub on ARM. There is a big advantage to reusing the > distro side tooling. If there isn''t really much reuse on the > bootloader side, then I''m fine with a different bootloader to Xen > interface. I would like to hear that from folks working on grub > though. > > > For u-boot Andre has proposed some syntactic sugar over the "fdt" > > command to make boot.scr more trivial to use. We would of course > > need to implement support for using it in the relevant distro tools > > (but they tend to be very distro/machine specific already, e.g. > > Debian''s flash-kernel) > > And being machine specific is a PITA. flash-kernel is certainly not > something we want to expand on. There is not much love for boot.scr > either. There is work to address what are not really machine > differences, but largely vendor u-boot differences: > > http://www.mail-archive.com/u-boot@lists.denx.de/msg119025.htmlu-boot still has quite a bit of work that needs to be done to make things standard across the board. I hope we will get there. but it will require vendors to update their u-boot builds. even for grub to be a viable option u-boot needs updated.> One option for u-boot which already supports syslinux style menu files > is to adopt the syslinux multiboot parsing support: > > http://www.syslinux.org/wiki/index.php/Doc/mbootI would like to have u-boot support more of syslinux than it does today.> > We need to back-up and consider what this looks like in the end for > all the pieces and get input from folks on grub, UEFI, and armv8. The > UEFI answer may be this is a grub problem. For armv8, this proposal > does match up well as the kernel boot interface for v8 is DT. Despite > some claims, ACPI will not completely replace DT because of this. > > Robgrub on arm still needs a bit of work. as does u-boot. ultimately having things look the same between x86 and arm for the user is the best option. so if u-boot supported syslinux''s mboot spec and grub supported the same syntax in both cases, regardless of if the implementation varied wildly, the API for lack of a better word should be consistent. Dennis -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.21 (GNU/Linux) iEYEARECAAYFAlIz4NMACgkQkSxm47BaWffX8QCgtSFFHfgHongecz9AESG43RsW /48An131lBoSmjwcJOlWNkQUxI3LXC5f =fQqh -----END PGP SIGNATURE-----
Andre Przywara
2013-Sep-16 17:01 UTC
Re: [PROPOSAL] ARM/FDT: passing multiple binaries to a kernel
On 09/15/2013 02:37 PM, Grant Likely wrote:> On Tue, 03 Sep 2013 17:53:44 +0200, Andre Przywara <andre.przywara@linaro.org> wrote: >> Hi, >> >> a normal Linux kernel currently supports reading the start and end >> address of a single binary blob via the FDT''s /chosen node. >> This will be interpreted as the location of an initial RAM disk. >> >> The Xen hypervisor itself is a kernel, but needs up to _two_ binaries >> for proper operation: a Dom0 Linux kernel and it''s associated initrd. >> On x86 this is solved via the multiboot protocol used by the Grub >> bootloader, which supports to pass an arbitrary number of binary modules >> to any kernel. >> >> Since in the ARM world we have the versatile device tree, we don''t need >> to implement the mulitboot protocol. >> >> So I''d like to propose a new binding which denotes binary modules a >> kernel can use at it''s own discretion. >> The need is triggered by the Xen hypervisor (which already uses a very >> similar scheme), but the approach is deliberately chosen to be as >> generic as possible to allow future uses (like passing firmware blobs >> for devices or the like). >> Credits for this go to Ian Campbell, who started something very similar >> [1] for the Xen hypervisor. The intention of this proposal is to make >> this generic and publicly documented. >> >> Looking forward to any comments! >> >> Thanks, >> Andre. >> >> [1] >> http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=docs/misc/arm/device-tree/booting.txt;h=94cd3f18a4e1317a35e1255bf5c6e1e091001d1a;hb=HEAD >> ---------------------------- >> * Multiple boot modules device tree bindings >> >> Boot loaders wanting to pass multiple additional binaries to a kernel >> shall add a node "module" for each binary blob under the /chosen node >> with the following properties: >> >> - compatible: >> compatible = "boot,module"; >> A bootloader may add names to more specifically describe the module, >> e.g. Xen may use "xen,dom0-kernel" or "xen,dom0-ramdisk". >> If possible a kernel should be able to use modules even without a >> descriptive naming, by enumerating them in order and using hard-coded >> meanings for each module (e.g. first is kernel, second is initrd). >> >> - reg: specifies the base physical address and size of a region in >> memory where the bootloader loaded the respective binary data to. >> >> - bootargs: >> An optional property describing arguments to use for this module. >> Could be a command line or configuration data. >> >> Example: >> /chosen { >> #size-cells = <0x1>; >> #address-cells = <0x1>; >> module@0 { >> compatible = "xen,linux-zimage", "xen,multiboot-module", >> "boot,module"; >> reg = <0x80000000 0x003dcff8>; >> bootargs = "console=hvc0 earlyprintk ro root=/dev/sda1 nosmp"; >> }; >> module@1 { >> compatible = "xen,linux-initrd", "xen,multiboot-module", >> "boot,module"; >> reg = <0x08000000 0x00123456>; >> };Grant, thanks for looking at this. Appreciate your comments.> The moment you pull in a ''reg'' property, your required to property parse > #size-cells and #address-cells and also ''ranges'' which is missing from > the above.You mean that early boot code has to read #size-cells and #address-cells and act accordingly when parsing the reg property? So just more code in early boot? But that would easily open the door for 64bit addresses for instance, right?> I don''t necessarily object to that, but it can be a lot to > ask for during early boot.I don''t think Xen in particular has a lot of problems with that. The DT implementation is quite capable (see Julien''s latest updates). > It also looks really weird in the chosen node. TBH this initrd syntax looks a bit weird to me in general, not following the nice and well defined DT way (no compatible, separate properties for start and length, ...)> For boot time artifacts like this, I''d rather see a duplication of > the linux,initrd- pattern. Something like: > /chosen { > xen,linux-zimage-start = <0x80000000>; > xen,linux-zimage-end = <0x803dcff8>; > linux,initrd-start = <0x8000000>; > linux,initrd-end = <0x8123456>; > }To me that sounds like a hack to avoid more coding work. The problem with that is that it would introduce a Xen specific property (actually two). So from a user''s perspective you want: a) generic properties to support future OSes without much hassle (using the DT''s compatible semantic) b) specifying load address and length in the normal way c) adding command lines d) potentially adding more arbitrary properties e) allowing an arbitrary number of modules To just go ahead with another hard-coded property to make life easier for us kernel level developers doesn''t sound very convincing to me. And especially supporting multiple modules would be very hackish then.> If have two reason for this; consistency and simplicity. Consistent > because it matches what Linux already uses,But this is actually not consistent with the rest of the DT architecture. Defining an own node for that looks like a perfect match to me in the DT world.> and really easy to parse > without mucking with ranges or #address/size-cells. The assumption is > that during early boot the system is dealing with a 1:1 mapped physical > address and there isn''t any bus translations that need to be processed.I see your point with early boot code constraints. But my idea was to create a flexible and generic solution, so that there will be a framework for bootloaders to specify blobs without needing updates every time someone comes up with a need for one. On x86 there was once such a need for microcode updates which couldn''t be easily satisfied because Linux/x86 itself does not support the multiboot protocol.> Question: what is the need for the xen,linux-initrd node? Why can''t the > existing "linux,initrd-*" properties continue to be used?The main driver for this was to avoid patching bootloaders just to boot Xen specifically. Rather we want to patch bootloaders to support some kind of "multiboot" protocol once and let Xen piggy-back on this. I think that is somewhat driven by experiences in the x86 world, were especially kernel people are reluctant to support something just for Xen''s need. Regards, Andre.