similar to: [PATCH 6/21] i386 Fixed pnp bios limits

PnP BIOS for x86 is part of drivers, so I missed it in the initial GDT page alignment patch. Kudos to Andrew for fixing that. Unfortunately, fixing the build introduced a kernel panic when trying to setup the as of yet unallocated GDTs for the APs. This fixes the problem by setting only the BSP's GDT, then copying the PnP segments back to the cpu_gdt_table template. Signed-off-by: Zachary

PnP BIOS for x86 is part of drivers, so I missed it in the initial GDT page alignment patch. Kudos to Andrew for fixing that. Unfortunately, fixing the build introduced a kernel panic when trying to setup the as of yet unallocated GDTs for the APs. This fixes the problem by setting only the BSP's GDT, then copying the PnP segments back to the cpu_gdt_table template. Signed-off-by: Zachary

Make GDT page aligned and page padded to support running inside of a hypervisor. This prevents false sharing of the GDT page with other hot data, which is not allowed in Xen, and causes performance problems in VMware. Rather than go back to the old method of statically allocating the GDT (which wastes unneded space for non-present CPUs), the GDT for APs is allocated dynamically. Signed-off-by:

Make GDT page aligned and page padded to support running inside of a hypervisor. This prevents false sharing of the GDT page with other hot data, which is not allowed in Xen, and causes performance problems in VMware. Rather than go back to the old method of statically allocating the GDT (which wastes unneded space for non-present CPUs), the GDT for APs is allocated dynamically. Signed-off-by:

Andrew Morton's fix for PnP BIOS. Signed-off-by: Zachary Amsden <zach@vmware.com> Index: linux-2.6.14-rc1/drivers/pnp/pnpbios/bioscalls.c =================================================================== --- linux-2.6.14-rc1.orig/drivers/pnp/pnpbios/bioscalls.c 2005-08-28 16:41:01.000000000 -0700 +++ linux-2.6.14-rc1/drivers/pnp/pnpbios/bioscalls.c 2005-09-28 13:13:42.000000000 -0700

Andrew Morton's fix for PnP BIOS. Signed-off-by: Zachary Amsden <zach@vmware.com> Index: linux-2.6.14-rc1/drivers/pnp/pnpbios/bioscalls.c =================================================================== --- linux-2.6.14-rc1.orig/drivers/pnp/pnpbios/bioscalls.c 2005-08-28 16:41:01.000000000 -0700 +++ linux-2.6.14-rc1/drivers/pnp/pnpbios/bioscalls.c 2005-09-28 13:13:42.000000000 -0700

Both the APM BIOS and PnP BIOS code use a segment hack to simulate real mode selector 0x40 (which points to the BIOS data area at 0x00400 in real mode). Several broken BIOSen use selector 0x40 as if they were running in real mode, which we make work by faking up selector 0x40 in the GDT to point to physical memory starting at 0x400. We limit the access to the remainder of this physical page

Both the APM BIOS and PnP BIOS code use a segment hack to simulate real mode selector 0x40 (which points to the BIOS data area at 0x00400 in real mode). Several broken BIOSen use selector 0x40 as if they were running in real mode, which we make work by faking up selector 0x40 in the GDT to point to physical memory starting at 0x400. We limit the access to the remainder of this physical page

Ancient inline assembler that manipulates descriptor tables is unreadable and has no type checking. Doing this in C actually generates better code, saves code space, and improves readability. The fact that you must cast descriptors to (char *) for the inline assembler to work properly caused me no end of grief working on these patches. Note that GCC does not generate rotations to utilize

Ancient inline assembler that manipulates descriptor tables is unreadable and has no type checking. Doing this in C actually generates better code, saves code space, and improves readability. The fact that you must cast descriptors to (char *) for the inline assembler to work properly caused me no end of grief working on these patches. Note that GCC does not generate rotations to utilize

It is impossible to have a zero length segment in descriptor tables using "normal" segments. One of many ways to properly protect segments to zero length is to map the base to an umapped page. Create a nicer way to do this, and stop subtracting 1 from the length passed to set_limit (note calling set limit with a zero limit does something very bad! - not anymore). Signed-off-by:

It is impossible to have a zero length segment in descriptor tables using "normal" segments. One of many ways to properly protect segments to zero length is to map the base to an umapped page. Create a nicer way to do this, and stop subtracting 1 from the length passed to set_limit (note calling set limit with a zero limit does something very bad! - not anymore). Signed-off-by:

Move PnP BIOS segment definitions into segment.h; the segments are reserved here, so they might as well be defined here as well. Note I didn't do this for APM BIOS, as Macintosh and other systems use those values to emulate APM in some scary way I don't want to understand. Signed-off-by: Zachary Amsden <zach@vmware.com> Index: linux-2.6.14-zach-work/include/asm-i386/segment.h

Move PnP BIOS segment definitions into segment.h; the segments are reserved here, so they might as well be defined here as well. Note I didn't do this for APM BIOS, as Macintosh and other systems use those values to emulate APM in some scary way I don't want to understand. Signed-off-by: Zachary Amsden <zach@vmware.com> Index: linux-2.6.14-zach-work/include/asm-i386/segment.h

The one remaining caller of set_limit, the PnP BIOS code, calls into the PnP BIOS, passing kernel parameters in and out. These parameteres may be passed from arbitrary kernel virtual memory, so they deserve strict protection to stop a bad BIOS from smashing beyond the object size. Unfortunately, the use of set_limit was badly botching this by setting the limit in terms of pages, when it really

The one remaining caller of set_limit, the PnP BIOS code, calls into the PnP BIOS, passing kernel parameters in and out. These parameteres may be passed from arbitrary kernel virtual memory, so they deserve strict protection to stop a bad BIOS from smashing beyond the object size. Unfortunately, the use of set_limit was badly botching this by setting the limit in terms of pages, when it really

I discovered an even more subtle problem; the PnP BIOS code is saving the %fs and %gs segments in inline assembler, yet it also uses the same hack for patching in a fake real mode selector for the BIOS data area. Note that the protected mode selector 0x40 overlaps the user TLS area in the GDT; this means that badly timed PnP BIOS calls could come in, save %fs, come back, and restore %fs -- to

I discovered an even more subtle problem; the PnP BIOS code is saving the %fs and %gs segments in inline assembler, yet it also uses the same hack for patching in a fake real mode selector for the BIOS data area. Note that the protected mode selector 0x40 overlaps the user TLS area in the GDT; this means that badly timed PnP BIOS calls could come in, save %fs, come back, and restore %fs -- to

Since APM BIOS segment limits are now fixed, set them in head.S GDT and don't use the complicated _set_limit() macro expansion. Signed-off-by: Zachary Amsden <zach@vmware.com> Index: linux-2.6.14-zach-work/arch/i386/kernel/head.S =================================================================== --- linux-2.6.14-zach-work.orig/arch/i386/kernel/head.S 2005-11-04 15:46:11.000000000 -0800

Since APM BIOS segment limits are now fixed, set them in head.S GDT and don't use the complicated _set_limit() macro expansion. Signed-off-by: Zachary Amsden <zach@vmware.com> Index: linux-2.6.14-zach-work/arch/i386/kernel/head.S =================================================================== --- linux-2.6.14-zach-work.orig/arch/i386/kernel/head.S 2005-11-04 15:46:11.000000000 -0800