On Mon, Nov 09, 2020 at 03:24:02PM -0800, Luck, Tony wrote:
> Booting as a guest under KVM results in error messages about
> unchecked MSR access:
>
> [ 6.814328][ T0] unchecked MSR access error: RDMSR from 0x17f at rIP: 0xffffffff84483f16 (mce_intel_feature_init+0x156/0x270)
>
> because KVM doesn't provide emulation for random model specific registers.
>
> Check for X86_FEATURE_HYPERVISOR and skip trying to enable the mode (a
> guest shouldn't be concerned with corrected errors anyway).
>
> Reported-by: Qian Cai <cai@xxxxxxxxxx>
> Fixes: 68299a42f842 ("x86/mce: Enable additional error logging on certain Intel CPUs")
> Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
> ---
> arch/x86/kernel/cpu/mce/intel.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/mce/intel.c b/arch/x86/kernel/cpu/mce/intel.c
> index b47883e364b4..7f7d863400b7 100644
> --- a/arch/x86/kernel/cpu/mce/intel.c
> +++ b/arch/x86/kernel/cpu/mce/intel.c
> @@ -517,6 +517,9 @@ static void intel_imc_init(struct cpuinfo_x86 *c)
> {
> u64 error_control;
>
> + if (boot_cpu_has(X86_FEATURE_HYPERVISOR))
> + return;
> +
Frankly, I'm tired of wagging the dog because the tail can't. If
qemu/kvm can't emulate a CPU model fully then it should ignore those
unknown MSR accesses by default, i.e., that "ignore_msrs" functionality
should be on by default I'd say...
We certainly can't be sprinkling this check everytime the kernel tries
to do something as basic as read an MSR.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
