linux/arch/x86
Linus Torvalds b6e61eef4f x86: Fix serialization in pit_expect_msb()
Wei Chong Tan reported a fast-PIT-calibration corner-case:

| pit_expect_msb() is vulnerable to SMI disturbance corner case
| in some platforms which causes /proc/cpuinfo to show wrong
| CPU MHz value when quick_pit_calibrate() jumps to success
| section.

I think that the real issue isn't even an SMI - but the fact
that in the very last iteration of the loop, there's no
serializing instruction _after_ the last 'rdtsc'. So even in
the absense of SMI's, we do have a situation where the cycle
counter was read without proper serialization.

The last check should be done outside the outer loop, since
_inside_ the outer loop, we'll be testing that the PIT has
the right MSB value has the right value in the next iteration.

So only the _last_ iteration is special, because that's the one
that will not check the PIT MSB value any more, and because the
final 'get_cycles()' isn't serialized.

In other words:

 - I'd like to move the PIT MSB check to after the last
   iteration, rather than in every iteration

 - I think we should comment on the fact that it's also a
   serializing instruction and so 'fences in' the TSC read.

Here's a suggested replacement.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Reported-by: "Tan, Wei Chong" <wei.chong.tan@intel.com>
Tested-by: "Tan, Wei Chong" <wei.chong.tan@intel.com>
LKML-Reference: <B28277FD4E0F9247A3D55704C440A140D5D683F3@pgsmsx504.gar.corp.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-08-10 19:56:57 +02:00
..
boot x86: fix usage of bios intcall() 2009-07-04 12:56:32 -07:00
configs Merge branch 'x86-kbuild-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2009-06-10 15:30:41 -07:00
crypto crypto: aes-ni - Remove CRYPTO_TFM_REQ_MAY_SLEEP from fpu template 2009-06-18 19:44:01 +08:00
ia32
include/asm Merge branch 'x86-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2009-08-04 15:28:59 -07:00
kernel x86: Fix serialization in pit_expect_msb() 2009-08-10 19:56:57 +02:00
kvm KVM: MMU: limit rmap chain length 2009-08-06 12:06:54 +03:00
lguest lguest: update commentry 2009-07-30 16:03:46 +09:30
lib x86, msr: execute on the correct CPU subset 2009-08-03 14:48:13 -07:00
math-emu
mm Merge branch 'x86-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2009-08-04 15:28:59 -07:00
oprofile x86/oprofile: rename kernel parameter for architectural perfmon to arch_perfmon 2009-07-10 05:22:50 +02:00
pci x86/pci: insert ioapic resource before assigning unassigned resources 2009-07-10 13:03:14 -07:00
power x86: Fix resume from suspend when CONFIG_CC_STACKPROTECTOR 2009-07-08 13:20:13 +02:00
vdso gcov: enable GCOV_PROFILE_ALL for x86_64 2009-06-18 13:03:58 -07:00
video
xen Merge branch 'x86-xen-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2009-06-10 16:16:27 -07:00
Kbuild
Kconfig intel-iommu: Restore DMAR_BROKEN_GFX_WA option for broken graphics drivers 2009-07-04 10:59:46 +01:00
Kconfig.cpu Revert "x86, bts: reenable ptrace branch trace support" 2009-06-11 00:32:00 +02:00
Kconfig.debug kmemcheck: make kconfig accessible for other architectures 2009-06-15 15:49:17 +02:00
Makefile kmemcheck: add the kmemcheck core 2009-06-13 15:37:30 +02:00
Makefile_32.cpu