Re: [PATCH 4/4] KVM: selftests: x86: Repeat the checking of xheader when IA32_XFD[18] is set in amx_test

[Sean Christopherson <seanjc@google.com>]

On Tue, Jan 10, 2023, Mingwei Zhang wrote:
> Repeat the checking of AMX component in xheader after xsavec when

s/xsavec/XSAVEC.  Not sure about xheader, though it seems like that should be
capitalized too.

> IA32_XFD[18] is set. This check calibrates the functionality scope of

s/18/XTILEDATA

> IA32_XFD: it does not intercept the XSAVE state management.

I didn't follow this.  Is this basically saying "Verify XTILEDATA is saved by
XSAVEC even when disabled via IA32_XFD"?

> Regardless of the values in IA32_XFD, AMX component state will still be
> managed by XSAVE* and XRSTOR* as long as XCR[18:17] are set.
> 
> Signed-off-by: Mingwei Zhang <mizhang@google.com>
> ---
>  tools/testing/selftests/kvm/x86_64/amx_test.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/tools/testing/selftests/kvm/x86_64/amx_test.c b/tools/testing/selftests/kvm/x86_64/amx_test.c
> index 18203e399e9d..9a80a59b64e6 100644
> --- a/tools/testing/selftests/kvm/x86_64/amx_test.c
> +++ b/tools/testing/selftests/kvm/x86_64/amx_test.c
> @@ -235,6 +235,16 @@ static void __attribute__((__flatten__)) guest_code(struct tile_config *amx_cfg,
>  
>  	/* xfd=0x40000, disable amx tiledata */
>  	wrmsr(MSR_IA32_XFD, XFEATURE_MASK_XTILEDATA);
> +
> +	/*
> +	 * Bit 18 is cleared in XSTATE_BV but set in XCOMP_BV, this property

s/Bit 18/XTILEDATA

> +	 * remains the same even when IA32_XFD disables amx tiledata.

I would phrase this as "even when AMX tile data is disabled via IA32_XFD".
Software disables AMX, IA32_XFD is the mechanic by which that is done.

> +	 */
> +	set_xstatebv(xsave_data, XFEATURE_MASK_XTILEDATA);
> +	__xsavec(xsave_data, XFEATURE_MASK_XTILEDATA);
> +	GUEST_ASSERT((get_xstatebv(xsave_data) & XFEATURE_MASK_XTILEDATA) == 0);
> +	GUEST_ASSERT((get_xcompbv(xsave_data) & XFEATURE_MASK_XTILEDATA) == XFEATURE_MASK_XTILEDATA);

Same feedback about using !(...) and unnecessary "== x".

> +
>  	GUEST_SYNC(6);
>  	GUEST_ASSERT(rdmsr(MSR_IA32_XFD) == XFEATURE_MASK_XTILEDATA);
>  	set_tilecfg(amx_cfg);
> -- 
> 2.39.0.314.g84b9a713c41-goog
>