linux-kernel - [PATCH 2/3] x86: KVM: VMX: cache guest written value of MSR_IA32

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Message-Id: <20250416002546.3300893-3-mlevitsk@redhat.com>
Date: Tue, 15 Apr 2025 20:25:45 -0400
From: Maxim Levitsky <mlevitsk@...hat.com>
To: kvm@...r.kernel.org
Cc: Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>,
	Paolo Bonzini <pbonzini@...hat.com>,
	x86@...nel.org,
	Sean Christopherson <seanjc@...gle.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>,
	linux-kernel@...r.kernel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH 2/3] x86: KVM: VMX: cache guest written value of MSR_IA32_DEBUGCTL

Store the guest's written value of MSR_IA32_DEBUGCTL in a software field,
insted of always reading/writing the GUEST_IA32_DEBUGCTL vmcs field.

This will allow in the future to have a different value in the
actual GUEST_IA32_DEBUGCTL from the value that the guest has set.

Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kvm/vmx/vmx.c | 5 ++++-
 arch/x86/kvm/vmx/vmx.h | 1 +
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 4237422dc4ed..c9208a4acda4 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2196,11 +2196,14 @@ static u64 vmx_get_supported_debugctl(struct kvm_vcpu *vcpu, bool host_initiated
 
 u64 vmx_get_guest_debugctl(struct kvm_vcpu *vcpu)
 {
-	return vmcs_read64(GUEST_IA32_DEBUGCTL);
+	return to_vmx(vcpu)->msr_ia32_debugctl;
 }
 
 static void __vmx_set_guest_debugctl(struct kvm_vcpu *vcpu, u64 data)
 {
+	struct vcpu_vmx *vmx = to_vmx(vcpu);
+
+	vmx->msr_ia32_debugctl = data;
 	vmcs_write64(GUEST_IA32_DEBUGCTL, data);
 }
 
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 8ac46fb47abd..699da6d2bc66 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -291,6 +291,7 @@ struct vcpu_vmx {
 	/* SGX Launch Control public key hash */
 	u64 msr_ia32_sgxlepubkeyhash[4];
 	u64 msr_ia32_mcu_opt_ctrl;
+	u64 msr_ia32_debugctl;
 	bool disable_fb_clear;
 
 	struct pt_desc pt_desc;
-- 
2.26.3