linux-kernel - [PATCH V2 02/12] KVM: x86: Allow the use of kvm_load_host_xsave_state() with guest_state

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Message-ID: <20250129095902.16391-3-adrian.hunter@intel.com>
Date: Wed, 29 Jan 2025 11:58:51 +0200
From: Adrian Hunter <adrian.hunter@...el.com>
To: pbonzini@...hat.com,
	seanjc@...gle.com
Cc: kvm@...r.kernel.org,
	rick.p.edgecombe@...el.com,
	kai.huang@...el.com,
	adrian.hunter@...el.com,
	reinette.chatre@...el.com,
	xiaoyao.li@...el.com,
	tony.lindgren@...ux.intel.com,
	binbin.wu@...ux.intel.com,
	dmatlack@...gle.com,
	isaku.yamahata@...el.com,
	nik.borisov@...e.com,
	linux-kernel@...r.kernel.org,
	yan.y.zhao@...el.com,
	chao.gao@...el.com,
	weijiang.yang@...el.com
Subject: [PATCH V2 02/12] KVM: x86: Allow the use of kvm_load_host_xsave_state() with guest_state_protected

From: Sean Christopherson <seanjc@...gle.com>

Allow the use of kvm_load_host_xsave_state() with
vcpu->arch.guest_state_protected == true. This will allow TDX to reuse
kvm_load_host_xsave_state() instead of creating its own version.

For consistency, amend kvm_load_guest_xsave_state() also.

Ensure that guest state that kvm_load_host_xsave_state() depends upon,
such as MSR_IA32_XSS, cannot be changed by user space, if
guest_state_protected.

[Adrian: wrote commit message]

Link: https://lore.kernel.org/r/Z2GiQS_RmYeHU09L@google.com
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
---
TD vcpu enter/exit v2:
 - New patch
---
 arch/x86/kvm/svm/svm.c |  7 +++++--
 arch/x86/kvm/x86.c     | 18 +++++++++++-------
 2 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 7640a84e554a..b4bcfe15ad5e 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4253,7 +4253,9 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu,
 		svm_set_dr6(svm, DR6_ACTIVE_LOW);
 
 	clgi();
-	kvm_load_guest_xsave_state(vcpu);
+
+	if (!vcpu->arch.guest_state_protected)
+		kvm_load_guest_xsave_state(vcpu);
 
 	kvm_wait_lapic_expire(vcpu);
 
@@ -4282,7 +4284,8 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu,
 	if (unlikely(svm->vmcb->control.exit_code == SVM_EXIT_NMI))
 		kvm_before_interrupt(vcpu, KVM_HANDLING_NMI);
 
-	kvm_load_host_xsave_state(vcpu);
+	if (!vcpu->arch.guest_state_protected)
+		kvm_load_host_xsave_state(vcpu);
 	stgi();
 
 	/* Any pending NMI will happen here */
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index bbb6b7f40b3a..5cf9f023fd4b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1169,11 +1169,9 @@ EXPORT_SYMBOL_GPL(kvm_lmsw);
 
 void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu)
 {
-	if (vcpu->arch.guest_state_protected)
-		return;
+	WARN_ON_ONCE(vcpu->arch.guest_state_protected);
 
 	if (kvm_is_cr4_bit_set(vcpu, X86_CR4_OSXSAVE)) {
-
 		if (vcpu->arch.xcr0 != kvm_host.xcr0)
 			xsetbv(XCR_XFEATURE_ENABLED_MASK, vcpu->arch.xcr0);
 
@@ -1192,13 +1190,11 @@ EXPORT_SYMBOL_GPL(kvm_load_guest_xsave_state);
 
 void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu)
 {
-	if (vcpu->arch.guest_state_protected)
-		return;
-
 	if (cpu_feature_enabled(X86_FEATURE_PKU) &&
 	    ((vcpu->arch.xcr0 & XFEATURE_MASK_PKRU) ||
 	     kvm_is_cr4_bit_set(vcpu, X86_CR4_PKE))) {
-		vcpu->arch.pkru = rdpkru();
+		if (!vcpu->arch.guest_state_protected)
+			vcpu->arch.pkru = rdpkru();
 		if (vcpu->arch.pkru != vcpu->arch.host_pkru)
 			wrpkru(vcpu->arch.host_pkru);
 	}
@@ -3916,6 +3912,10 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		if (!msr_info->host_initiated &&
 		    !guest_cpuid_has(vcpu, X86_FEATURE_XSAVES))
 			return 1;
+
+		if (vcpu->arch.guest_state_protected)
+			return 1;
+
 		/*
 		 * KVM supports exposing PT to the guest, but does not support
 		 * IA32_XSS[bit 8]. Guests have to use RDMSR/WRMSR rather than
@@ -4375,6 +4375,10 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		if (!msr_info->host_initiated &&
 		    !guest_cpuid_has(vcpu, X86_FEATURE_XSAVES))
 			return 1;
+
+		if (vcpu->arch.guest_state_protected)
+			return 1;
+
 		msr_info->data = vcpu->arch.ia32_xss;
 		break;
 	case MSR_K7_CLK_CTL:
-- 
2.43.0