linux-kernel - [PATCH v3 20/27] KVM: x86: Allow WRMSRNS to be advertised to guests

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Message-ID: <20241001050110.3643764-21-xin@zytor.com>
Date: Mon, 30 Sep 2024 22:01:03 -0700
From: "Xin Li (Intel)" <xin@...or.com>
To: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org
Cc: seanjc@...gle.com, pbonzini@...hat.com, corbet@....net, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, hpa@...or.com, luto@...nel.org, peterz@...radead.org,
        andrew.cooper3@...rix.com, xin@...or.com
Subject: [PATCH v3 20/27] KVM: x86: Allow WRMSRNS to be advertised to guests

From: Xin Li <xin3.li@...el.com>

Allow WRMSRNS to be advertised to guests.

WRMSRNS behaves exactly like WRMSR with the only difference being
that it is not a serializing instruction by default.  It improves
performance when being used in a hot path, e.g., setting FRED RSP0.

Signed-off-by: Xin Li <xin3.li@...el.com>
Signed-off-by: Xin Li (Intel) <xin@...or.com>
Tested-by: Shan Kang <shan.kang@...el.com>
---
 arch/x86/kvm/cpuid.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index c55d150ece8d..63a78ebf9482 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -700,7 +700,7 @@ void kvm_set_cpu_caps(void)
 	kvm_cpu_cap_mask(CPUID_7_1_EAX,
 		F(AVX_VNNI) | F(AVX512_BF16) | F(CMPCCXADD) |
 		F(FZRM) | F(FSRS) | F(FSRC) | F(FRED) | F(LKGS) |
-		F(AMX_FP16) | F(AVX_IFMA) | F(LAM)
+		F(WRMSRNS) | F(AMX_FP16) | F(AVX_IFMA) | F(LAM)
 	);
 
 	kvm_cpu_cap_init_kvm_defined(CPUID_7_1_EDX,
-- 
2.46.2