Re: [PATCH v2 2/7] KVM: selftests: x86: Fix an error in comment of amx_test

[Chao Gao <chao.gao@intel.com>]

On Tue, Feb 14, 2023 at 06:46:01PM +0000, Mingwei Zhang wrote:
>After the execution of __tilerelease(), AMX component will be in INIT
>state. Therefore, execution of XSAVEC saving the AMX state into memory will
>cause the xstate_bv[18] cleared in xheader. However, the xcomp_bv[18] will
>remain set. Fix the error in comment. Also, update xsavec() to XSAVEC
>because xcomp_bv[18] is set due to the instruction, not the function.
>Finally, use XTILEDATA instead 'bit 18' in comments.
>
>Cc: Jim Mattson <jmattson@google.com>
>Cc: Venkatesh Srinivas <venkateshs@google.com>
>Cc: Aaron Lewis <aaronlewis@google.com>
>Signed-off-by: Mingwei Zhang <mizhang@google.com>
>---
> tools/testing/selftests/kvm/x86_64/amx_test.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
>diff --git a/tools/testing/selftests/kvm/x86_64/amx_test.c b/tools/testing/selftests/kvm/x86_64/amx_test.c
>index d506821a5a26..aac727ff7cf8 100644
>--- a/tools/testing/selftests/kvm/x86_64/amx_test.c
>+++ b/tools/testing/selftests/kvm/x86_64/amx_test.c
>@@ -190,7 +190,10 @@ static void __attribute__((__flatten__)) guest_code(struct tile_config *amx_cfg,
> 	GUEST_SYNC(4);
> 	__tilerelease();
> 	GUEST_SYNC(5);
>-	/* bit 18 not in the XCOMP_BV after xsavec() */
>+	/*
>+	 * After XSAVEC, XTILEDATA is cleared in the xstate_bv but is set in
>+	 * the xcomp_bv.
>+	 */
> 	xstate->header.xstate_bv = XFEATURE_MASK_XTILEDATA;
> 	__xsavec(xstate, XFEATURE_MASK_XTILEDATA);
> 	GUEST_ASSERT(!(xstate->header.xstate_bv & XFEATURE_MASK_XTILEDATA));

maybe it would be better to add another GUEST_ASSERT() to enforce that
XTILEDATA is set in the xcomp_bv.

>-- 
>2.39.1.581.gbfd45094c4-goog
>