Re: [PATCH v2 3/7] KVM: selftests: x86: Add check of CR0.TS in the #NM handler in amx_test

[Aaron Lewis]

On Tue, Feb 14, 2023 at 6:46 PM Mingwei Zhang <mizhang@xxxxxxxxxx> wrote:
>
> Add check of CR0.TS[bit 3] before the check of IA32_XFD_ERR in the #NM
> handler in amx_test. This is because XFD may not be the only reason of
> the IA32_XFD MSR and the bitmap corresponding to the state components
> required by the faulting instruction." (Intel SDM vol 1. Section 13.14)
>
> Add the missing check of CR0.TS.
>
> Signed-off-by: Mingwei Zhang <mizhang@xxxxxxxxxx>
> ---
>  tools/testing/selftests/kvm/x86_64/amx_test.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/tools/testing/selftests/kvm/x86_64/amx_test.c b/tools/testing/selftests/kvm/x86_64/amx_test.c
> index aac727ff7cf8..847752998660 100644
> --- a/tools/testing/selftests/kvm/x86_64/amx_test.c
> +++ b/tools/testing/selftests/kvm/x86_64/amx_test.c
> @@ -215,6 +215,7 @@ void guest_nm_handler(struct ex_regs *regs)
>  {
>         /* Check if #NM is triggered by XFEATURE_MASK_XTILEDATA */
>         GUEST_SYNC(7);
> +       GUEST_ASSERT((get_cr0() & X86_CR0_TS) == 0);

Can't we infer that the #NM is the result of an XFD error due to the fact
that IA32_XFD_ERR is set?  Is this check needed?
SDM vol 1, 13.14, EXTENDED FEATURE DISABLE (XFD)
 - Device-not-available exceptions that are not due to XFD - those
   resulting from setting CR0.TS to 1 - do not modify the IA32_XFD_ERR
   MSR.

>         GUEST_ASSERT(rdmsr(MSR_IA32_XFD_ERR) == XFEATURE_MASK_XTILEDATA);
>         GUEST_SYNC(8);
>         GUEST_ASSERT(rdmsr(MSR_IA32_XFD_ERR) == XFEATURE_MASK_XTILEDATA);
> --
> 2.39.1.581.gbfd45094c4-goog
>