linux-kernel - [RFC PATCH 3/9] KVM: x86: Add a kvm-only leaf for BHI

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Message-Id: <20221210160046.2608762-4-chen.zhang@intel.com>
Date:   Sun, 11 Dec 2022 00:00:40 +0800
From:   Zhang Chen <chen.zhang@...el.com>
To:     x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Zhang Chen <chen.zhang@...el.com>, Chao Gao <chao.gao@...el.com>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: [RFC PATCH 3/9] KVM: x86: Add a kvm-only leaf for BHI_CTRL

KVM needs to check if guests can see BHI_CTRL. If a guest is using
BHB-clearing sequence and cannot see BHI_CTRL and the host enumerates BHI,
KVM is responsible for setting BHI_DIS_S for the guest.

This allows VM migration from parts doesn't enumerate BHI to those
that enumerate BHI.

Signed-off-by: Zhang Chen <chen.zhang@...el.com>
---
 arch/x86/kvm/cpuid.c         | 2 +-
 arch/x86/kvm/reverse_cpuid.h | 2 ++
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 8d45bc0b4b7c..91af27cc57e5 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -669,7 +669,7 @@ void kvm_set_cpu_caps(void)
 	);
 
 	kvm_cpu_cap_init_scattered(CPUID_7_2_EDX,
-		SF(RRSBA_CTRL)
+		SF(RRSBA_CTRL) | F(BHI_CTRL)
 	);
 
 	kvm_cpu_cap_mask(CPUID_8000_0001_ECX,
diff --git a/arch/x86/kvm/reverse_cpuid.h b/arch/x86/kvm/reverse_cpuid.h
index 4c38ed61c505..cf4e209ce2f6 100644
--- a/arch/x86/kvm/reverse_cpuid.h
+++ b/arch/x86/kvm/reverse_cpuid.h
@@ -27,6 +27,8 @@ enum kvm_only_cpuid_leafs {
 
 /* Intel-defined sub-features, CPUID level 0x00000007:2 (EDX)*/
 #define KVM_X86_FEATURE_RRSBA_CTRL	KVM_X86_FEATURE(CPUID_7_2_EDX, 2)
+/* X86_FEATURE_BHI_CTRL only used by KVM */
+#define X86_FEATURE_BHI_CTRL		KVM_X86_FEATURE(CPUID_7_2_EDX, 4)
 
 struct cpuid_reg {
 	u32 function;
-- 
2.25.1