linux-kernel - [PATCH 9/9] KVM: x86: Restrict XSAVE in cpu

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Date:   Fri, 10 Nov 2023 15:55:28 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH 9/9] KVM: x86: Restrict XSAVE in cpu_caps based on KVM capabilities

Restrict XSAVE in guest cpu_caps so that XSAVES dependencies on XSAVE are
automatically handled instead of manually checking for host and guest
XSAVE support.  Aside from modifying XSAVE in cpu_caps, this should be a
glorified nop as KVM doesn't query guest XSAVE support (which is also why
it wasn't/isn't a bug to leave XSAVE set in guest CPUID).

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/svm/svm.c | 2 +-
 arch/x86/kvm/vmx/vmx.c | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 9e3a9191dac1..6fe2d7bf4959 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4315,8 +4315,8 @@ static void svm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 	 * XSS on VM-Enter/VM-Exit.  Failure to do so would effectively give
 	 * the guest read/write access to the host's XSS.
 	 */
+	guest_cpu_cap_restrict(vcpu, X86_FEATURE_XSAVE);
 	guest_cpu_cap_change(vcpu, X86_FEATURE_XSAVES,
-			     boot_cpu_has(X86_FEATURE_XSAVE) &&
 			     boot_cpu_has(X86_FEATURE_XSAVES) &&
 			     guest_cpu_cap_has(vcpu, X86_FEATURE_XSAVE));
 
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 815692dc0aff..7645945af5c5 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7752,8 +7752,8 @@ static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 	 * to the guest.  XSAVES depends on CR4.OSXSAVE, and CR4.OSXSAVE can be
 	 * set if and only if XSAVE is supported.
 	 */
-	if (boot_cpu_has(X86_FEATURE_XSAVE) &&
-	    guest_cpu_cap_has(vcpu, X86_FEATURE_XSAVE))
+	guest_cpu_cap_restrict(vcpu, X86_FEATURE_XSAVE);
+	if (guest_cpu_cap_has(vcpu, X86_FEATURE_XSAVE))
 		guest_cpu_cap_restrict(vcpu, X86_FEATURE_XSAVES);
 	else
 		guest_cpu_cap_clear(vcpu, X86_FEATURE_XSAVES);
-- 
2.42.0.869.gea05f2083d-goog