linux-kernel - [PATCH 2/4] KVM: selftests: x86: Add check of IA32_XFD in amx

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Date:   Tue, 10 Jan 2023 18:58:21 +0000
From:   Mingwei Zhang <mizhang@...gle.com>
To:     kvm@...r.kernel.org
Cc:     linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jim Mattson <jmattson@...gle.com>,
        Venkatesh Srinivas <venkateshs@...gle.com>,
        Aaron Lewis <aaronlewis@...gle.com>,
        Mingwei Zhang <mizhang@...gle.com>
Subject: [PATCH 2/4] KVM: selftests: x86: Add check of IA32_XFD in amx_test

When #NM is triggered, the handler needs to ensure the exception is
triggered by AMX by checking IA32_XFD_ERR and not because of CR0.TS[bit 3]
is 1. Note that the value of IA32_XFD_ERR comes from "the logical AND 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 before checking the value of IA32_XFD_ERR.
In addition, add an extra check to IA32_XFD to ensure the behavior is
consistent with the AMX archtecture. In addition, repeat the checks across
context switch to ensure the values of IA32_XFD and IA32_XFD_ERR are well
preserved.

Signed-off-by: Mingwei Zhang <mizhang@...gle.com>
---
 tools/testing/selftests/kvm/x86_64/amx_test.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/testing/selftests/kvm/x86_64/amx_test.c b/tools/testing/selftests/kvm/x86_64/amx_test.c
index 16533949a189..b2369f956fea 100644
--- a/tools/testing/selftests/kvm/x86_64/amx_test.c
+++ b/tools/testing/selftests/kvm/x86_64/amx_test.c
@@ -226,9 +226,12 @@ 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);
 	GUEST_ASSERT(rdmsr(MSR_IA32_XFD_ERR) == XFEATURE_MASK_XTILEDATA);
+	GUEST_ASSERT((rdmsr(MSR_IA32_XFD) & XFEATURE_MASK_XTILEDATA) == XFEATURE_MASK_XTILEDATA);
 	GUEST_SYNC(8);
 	GUEST_ASSERT(rdmsr(MSR_IA32_XFD_ERR) == XFEATURE_MASK_XTILEDATA);
+	GUEST_ASSERT((rdmsr(MSR_IA32_XFD) & XFEATURE_MASK_XTILEDATA) == XFEATURE_MASK_XTILEDATA);
 	/* Clear xfd_err */
 	wrmsr(MSR_IA32_XFD_ERR, 0);
 	/* xfd=0, enable amx */
-- 
2.39.0.314.g84b9a713c41-goog