linux-kernel - [RFC PATCH v2 09/11] KVM: VMX: Advertise MITI_CTRL_BHB_CLEAR_SEQ_S

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Date:   Fri, 14 Apr 2023 14:25:30 +0800
From:   Chao Gao <chao.gao@...el.com>
To:     kvm@...r.kernel.org
Cc:     Jiaan Lu <jiaan.lu@...el.com>, Zhang Chen <chen.zhang@...el.com>,
        Chao Gao <chao.gao@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: [RFC PATCH v2 09/11] KVM: VMX: Advertise MITI_CTRL_BHB_CLEAR_SEQ_S_SUPPORT

From: Zhang Chen <chen.zhang@...el.com>

Allow guest to query if the underying VMM understands BHB-clearing
sequence and report the statue of BHB-clearing sequence in suprevisor
mode i.e. CPL < 3 via MSR_VIRTUAL_MITIGATION_ENUM/CTRL.

Enable BHI_DIS_S for guest if guest is using BHI-clearing sequence and
the sequence isn't effective on the processor.

Signed-off-by: Zhang Chen <chen.zhang@...el.com>
Signed-off-by: Chao Gao <chao.gao@...el.com>
Tested-by: Jiaan Lu <jiaan.lu@...el.com>
---
 arch/x86/kvm/vmx/vmx.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 25afb4c3e55e..abbbf8e66b53 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1944,8 +1944,10 @@ static inline bool is_vmx_feature_control_msr_valid(struct vcpu_vmx *vmx,
 }
 
 #define VIRTUAL_ENUMERATION_VALID_BITS	VIRT_ENUM_MITIGATION_CTRL_SUPPORT
-#define MITI_ENUM_VALID_BITS		MITI_ENUM_RETPOLINE_S_SUPPORT
-#define MITI_CTRL_VALID_BITS		MITI_CTRL_RETPOLINE_S_USED
+#define MITI_ENUM_VALID_BITS		(MITI_ENUM_RETPOLINE_S_SUPPORT | \
+					 MITI_ENUM_BHB_CLEAR_SEQ_S_SUPPORT)
+#define MITI_CTRL_VALID_BITS		(MITI_CTRL_RETPOLINE_S_USED | \
+					 MITI_CTRL_BHB_CLEAR_SEQ_S_USED)
 
 static int vmx_get_msr_feature(struct kvm_msr_entry *msr)
 {
@@ -2496,6 +2498,11 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		    arch_msr & ARCH_CAP_RRSBA)
 			spec_ctrl_mask |= SPEC_CTRL_RRSBA_DIS_S;
 
+		if (data & MITI_CTRL_BHB_CLEAR_SEQ_S_USED &&
+		    kvm_cpu_cap_has(X86_FEATURE_BHI_CTRL) &&
+		    !(arch_msr & ARCH_CAP_BHI_NO))
+			spec_ctrl_mask |= SPEC_CTRL_BHI_DIS_S;
+
 		/*
 		 * Intercept IA32_SPEC_CTRL to disallow guest from changing
 		 * certain bits.
-- 
2.40.0