Commit-ID: 37c528ee1af7f24eb31f4195b8b7d4f23e6c716d
Gitweb: http://git.kernel.org/tip/37c528ee1af7f24eb31f4195b8b7d4f23e6c716d
Author: Wanpeng Li <[email protected]>
AuthorDate: Wed, 22 Jun 2016 09:28:28 +0800
Committer: Ingo Molnar <[email protected]>
CommitDate: Mon, 11 Jul 2016 09:20:36 +0200
x86/tsc_msr: Fix rdmsr(MSR_PLATFORM_INFO) unsafe warning in KVM guest
After this commit:
fc273eeef314 ("x86/tsc_msr: Extend to include Intel Core Architecture")
The following unsafe MSR reading warning triggers:
WARNING: CPU: 0 PID: 0 at arch/x86/mm/extable.c:50
ex_handler_rdmsr_unsafe+0x6a/0x70
unchecked MSR access error: RDMSR from 0xce
Call Trace:
dump_stack+0x67/0x99
__warn+0xd1/0xf0
warn_slowpath_fmt+0x4f/0x60
ex_handler_rdmsr_unsafe+0x6a/0x70
fixup_exception+0x39/0x50
do_general_protection+0x93/0x1b0
general_protection+0x22/0x30
? cpu_khz_from_msr+0xd8/0x1c0
native_calibrate_cpu+0x30/0x5b0
tsc_init+0x2b/0x297
x86_late_time_init+0xf/0x11
start_kernel+0x398/0x451
? set_init_arg+0x55/0x55
x86_64_start_reservations+0x2f/0x31
x86_64_start_kernel+0xea/0xed
As Radim pointed out before:
| MSR_PLATFORM_INFO: Intel changes it from family to family and there is
| no obvious overlap or default. If we picked 0 (any other fixed value),
| then the guest would have to know that 0 doesn't mean that
| MSR_PLATFORM_INFO returned 0, but that KVM doesn't emulate this MSR and
| the value cannot be used. This is very similar to handling a #GP in the
| guest, but also has a disadvantage, because KVM cannot say that
| MSR_PLATFORM_INFO is 0. Simple emulation is not possible.
Fix it by using rdmsr_safe(MSR_PLATFORM_INFO) in KVM guest to
not trigger a #GP, then tsc will be calibrated by a fallback
method: PIT, HPET etc.
Reported-by: kernel test robot <[email protected]>
Signed-off-by: Wanpeng Li <[email protected]>
Acked-by: Paolo Bonzini <[email protected]>
Cc: Chen Yu <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Len Brown <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Linux PM list <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Radim Krčmář <[email protected]>
Cc: Rafael J. Wysocki <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Zhang Rui <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Link:
http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
---
arch/x86/kernel/tsc_msr.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/tsc_msr.c b/arch/x86/kernel/tsc_msr.c
index e0c2b30..e6e465e 100644
--- a/arch/x86/kernel/tsc_msr.c
+++ b/arch/x86/kernel/tsc_msr.c
@@ -70,7 +70,7 @@ static int match_cpu(u8 family, u8 model)
*/
unsigned long cpu_khz_from_msr(void)
{
- u32 lo, hi, ratio, freq_id, freq;
+ u32 lo, hi, freq_id, freq, ratio = 0;
unsigned long res;
int cpu_index;
@@ -123,8 +123,8 @@ unsigned long cpu_khz_from_msr(void)
}
get_ratio:
- rdmsr(MSR_PLATFORM_INFO, lo, hi);
- ratio = (lo >> 8) & 0xff;
+ if (!rdmsr_safe(MSR_PLATFORM_INFO, &lo, &hi))
+ ratio = (lo >> 8) & 0xff;
done:
/* TSC frequency = maximum resolved freq * maximum resolved bus ratio */
