On 17/02/2020 1:01 pm, Michael S. Tsirkin wrote:> On Mon, Feb 17, 2020 at 10:01:07AM +0100, Jean-Philippe Brucker wrote: >> On Sun, Feb 16, 2020 at 04:50:33AM -0500, Michael S. Tsirkin wrote: >>> On Fri, Feb 14, 2020 at 04:57:11PM +0000, Robin Murphy wrote: >>>> On 14/02/2020 4:04 pm, Jean-Philippe Brucker wrote: >>>>> With the built-in topology description in place, x86 platforms can now >>>>> use the virtio-iommu. >>>>> >>>>> Signed-off-by: Jean-Philippe Brucker <jean-philippe at linaro.org> >>>>> --- >>>>> drivers/iommu/Kconfig | 3 ++- >>>>> 1 file changed, 2 insertions(+), 1 deletion(-) >>>>> >>>>> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig >>>>> index 068d4e0e3541..adcbda44d473 100644 >>>>> --- a/drivers/iommu/Kconfig >>>>> +++ b/drivers/iommu/Kconfig >>>>> @@ -508,8 +508,9 @@ config HYPERV_IOMMU >>>>> config VIRTIO_IOMMU >>>>> bool "Virtio IOMMU driver" >>>>> depends on VIRTIO=y >>>>> - depends on ARM64 >>>>> + depends on (ARM64 || X86) >>>>> select IOMMU_API >>>>> + select IOMMU_DMA >>>> >>>> Can that have an "if X86" for clarity? AIUI it's not necessary for >>>> virtio-iommu itself (and really shouldn't be), but is merely to satisfy the >>>> x86 arch code's expectation that IOMMU drivers bring their own DMA ops, >>>> right? >>>> >>>> Robin. >>> >>> In fact does not this work on any platform now? >> >> There is ongoing work to use the generic IOMMU_DMA ops on X86. AMD IOMMU >> has been converted recently [1] but VT-d still implements its own DMA ops >> (conversion patches are on the list [2]). On Arm the arch Kconfig selects >> IOMMU_DMA, and I assume we'll have the same on X86 once Tom's work is >> complete. Until then I can add a "if X86" here for clarity. >> >> Thanks, >> Jean >> >> [1] https://lore.kernel.org/linux-iommu/20190613223901.9523-1-murphyt7 at tcd.ie/ >> [2] https://lore.kernel.org/linux-iommu/20191221150402.13868-1-murphyt7 at tcd.ie/ > > What about others? E.g. PPC?That was the point I was getting at - while iommu-dma should build just fine for the likes of PPC, s390, 32-bit Arm, etc., they have no architecture code to correctly wire up iommu_dma_ops to devices. Thus there's currently no point pulling it in and pretending it's anything more than a waste of space for architectures other than arm64 and x86. It's merely a historical artefact of the x86 DMA API implementation that when the IOMMU drivers were split out to form drivers/iommu they took some of their relevant arch code with them. Robin.
On Mon, Feb 17, 2020 at 01:22:44PM +0000, Robin Murphy wrote:> On 17/02/2020 1:01 pm, Michael S. Tsirkin wrote: > > On Mon, Feb 17, 2020 at 10:01:07AM +0100, Jean-Philippe Brucker wrote: > > > On Sun, Feb 16, 2020 at 04:50:33AM -0500, Michael S. Tsirkin wrote: > > > > On Fri, Feb 14, 2020 at 04:57:11PM +0000, Robin Murphy wrote: > > > > > On 14/02/2020 4:04 pm, Jean-Philippe Brucker wrote: > > > > > > With the built-in topology description in place, x86 platforms can now > > > > > > use the virtio-iommu. > > > > > > > > > > > > Signed-off-by: Jean-Philippe Brucker <jean-philippe at linaro.org> > > > > > > --- > > > > > > drivers/iommu/Kconfig | 3 ++- > > > > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > > > > > > > diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig > > > > > > index 068d4e0e3541..adcbda44d473 100644 > > > > > > --- a/drivers/iommu/Kconfig > > > > > > +++ b/drivers/iommu/Kconfig > > > > > > @@ -508,8 +508,9 @@ config HYPERV_IOMMU > > > > > > config VIRTIO_IOMMU > > > > > > bool "Virtio IOMMU driver" > > > > > > depends on VIRTIO=y > > > > > > - depends on ARM64 > > > > > > + depends on (ARM64 || X86) > > > > > > select IOMMU_API > > > > > > + select IOMMU_DMA > > > > > > > > > > Can that have an "if X86" for clarity? AIUI it's not necessary for > > > > > virtio-iommu itself (and really shouldn't be), but is merely to satisfy the > > > > > x86 arch code's expectation that IOMMU drivers bring their own DMA ops, > > > > > right? > > > > > > > > > > Robin. > > > > > > > > In fact does not this work on any platform now? > > > > > > There is ongoing work to use the generic IOMMU_DMA ops on X86. AMD IOMMU > > > has been converted recently [1] but VT-d still implements its own DMA ops > > > (conversion patches are on the list [2]). On Arm the arch Kconfig selects > > > IOMMU_DMA, and I assume we'll have the same on X86 once Tom's work is > > > complete. Until then I can add a "if X86" here for clarity. > > > > > > Thanks, > > > Jean > > > > > > [1] https://lore.kernel.org/linux-iommu/20190613223901.9523-1-murphyt7 at tcd.ie/ > > > [2] https://lore.kernel.org/linux-iommu/20191221150402.13868-1-murphyt7 at tcd.ie/ > > > > What about others? E.g. PPC? > > That was the point I was getting at - while iommu-dma should build just fine > for the likes of PPC, s390, 32-bit Arm, etc., they have no architecture code > to correctly wire up iommu_dma_ops to devices. Thus there's currently no > point pulling it in and pretending it's anything more than a waste of space > for architectures other than arm64 and x86. It's merely a historical > artefact of the x86 DMA API implementation that when the IOMMU drivers were > split out to form drivers/iommu they took some of their relevant arch code > with them. > > Robin.Rather than white-listing architectures, how about making the architectures in question set some kind of symbol, and depend on it? -- MST
On 17/02/2020 1:31 pm, Michael S. Tsirkin wrote:> On Mon, Feb 17, 2020 at 01:22:44PM +0000, Robin Murphy wrote: >> On 17/02/2020 1:01 pm, Michael S. Tsirkin wrote: >>> On Mon, Feb 17, 2020 at 10:01:07AM +0100, Jean-Philippe Brucker wrote: >>>> On Sun, Feb 16, 2020 at 04:50:33AM -0500, Michael S. Tsirkin wrote: >>>>> On Fri, Feb 14, 2020 at 04:57:11PM +0000, Robin Murphy wrote: >>>>>> On 14/02/2020 4:04 pm, Jean-Philippe Brucker wrote: >>>>>>> With the built-in topology description in place, x86 platforms can now >>>>>>> use the virtio-iommu. >>>>>>> >>>>>>> Signed-off-by: Jean-Philippe Brucker <jean-philippe at linaro.org> >>>>>>> --- >>>>>>> drivers/iommu/Kconfig | 3 ++- >>>>>>> 1 file changed, 2 insertions(+), 1 deletion(-) >>>>>>> >>>>>>> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig >>>>>>> index 068d4e0e3541..adcbda44d473 100644 >>>>>>> --- a/drivers/iommu/Kconfig >>>>>>> +++ b/drivers/iommu/Kconfig >>>>>>> @@ -508,8 +508,9 @@ config HYPERV_IOMMU >>>>>>> config VIRTIO_IOMMU >>>>>>> bool "Virtio IOMMU driver" >>>>>>> depends on VIRTIO=y >>>>>>> - depends on ARM64 >>>>>>> + depends on (ARM64 || X86) >>>>>>> select IOMMU_API >>>>>>> + select IOMMU_DMA >>>>>> >>>>>> Can that have an "if X86" for clarity? AIUI it's not necessary for >>>>>> virtio-iommu itself (and really shouldn't be), but is merely to satisfy the >>>>>> x86 arch code's expectation that IOMMU drivers bring their own DMA ops, >>>>>> right? >>>>>> >>>>>> Robin. >>>>> >>>>> In fact does not this work on any platform now? >>>> >>>> There is ongoing work to use the generic IOMMU_DMA ops on X86. AMD IOMMU >>>> has been converted recently [1] but VT-d still implements its own DMA ops >>>> (conversion patches are on the list [2]). On Arm the arch Kconfig selects >>>> IOMMU_DMA, and I assume we'll have the same on X86 once Tom's work is >>>> complete. Until then I can add a "if X86" here for clarity. >>>> >>>> Thanks, >>>> Jean >>>> >>>> [1] https://lore.kernel.org/linux-iommu/20190613223901.9523-1-murphyt7 at tcd.ie/ >>>> [2] https://lore.kernel.org/linux-iommu/20191221150402.13868-1-murphyt7 at tcd.ie/ >>> >>> What about others? E.g. PPC? >> >> That was the point I was getting at - while iommu-dma should build just fine >> for the likes of PPC, s390, 32-bit Arm, etc., they have no architecture code >> to correctly wire up iommu_dma_ops to devices. Thus there's currently no >> point pulling it in and pretending it's anything more than a waste of space >> for architectures other than arm64 and x86. It's merely a historical >> artefact of the x86 DMA API implementation that when the IOMMU drivers were >> split out to form drivers/iommu they took some of their relevant arch code >> with them. >> >> Robin. > > > Rather than white-listing architectures, how about making the > architectures in question set some kind of symbol, and depend on it?Umm, that's basically what we have already? Architectures that use iommu_dma_ops select IOMMU_DMA. The only issue is the oddity of x86 treating IOMMU drivers as part of its arch code, which has never come up against a cross-architecture driver until now. Hence the options of either maintaining that paradigm and having the 'x86 arch code' aspect of this driver "select IOMMU_DMA if x86" such that it works out equivalent to AMD_IOMMU, or a more involved cleanup to move that responsibility out of drivers/iommu/Kconfig entirely and have arch/x86/Kconfig do something like "select IOMMU_DMA if IOMMU_API", as Jean suggested up-thread. In the specific context of IOMMU_DMA we're not talking about any kind of white-list, merely a one-off special case for one particular architecture. Robin.