From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
------------[ cut here ]------------
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
Modules linked in:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.7.0-rc3+ #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
0000000000000000 ffffffff81c03ce0 ffffffff813b3eae ffffffff81c03d30
0000000000000000 ffffffff81c03d20 ffffffff81067181 0000003200000001
ffffffff81c03df8 ffffffff8179676c 0000000000000000 ffffffff81fcd2c0
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
After commit (fc141535ad8 : "x86 tsc_msr: Extend to include Intel Core
Architecture"), rdmsr MSR_PLATFORM_INFO is used to get maximum non-turbo
ratio for recent Intel Core Architecture which results in kvm guest rdmsr
unsafe warning.
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.
This patch fix it by using rdmsr_safe to read MSR_PLATFORM_INFO in kvm
guest in order that #GP can be fixed up, then tsc will be calibrated by
PIT, HPET etc.
Reported-by: kernel test robot <xiaolong.ye@xxxxxxxxx>
Cc: Len Brown <len.brown@xxxxxxxxx>
Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
Cc: Zhang Rui <rui.zhang@xxxxxxxxx>
Cc: Chen Yu <y.c.chen@xxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
Cc: jacob.jun.pan@xxxxxxxxx
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
---
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 */
--
1.9.1
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