linux-kernel - [PATCH v3 09/22] kvm: x86: Enable dynamic XSAVE features at KVM_SET

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Date:   Wed, 22 Dec 2021 04:40:39 -0800
From:   Jing Liu <jing2.liu@...el.com>
To:     x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, pbonzini@...hat.com, corbet@....net,
        shuah@...nel.org
Cc:     seanjc@...gle.com, jun.nakajima@...el.com, kevin.tian@...el.com,
        jing2.liu@...ux.intel.com, jing2.liu@...el.com,
        guang.zeng@...el.com, wei.w.wang@...el.com, yang.zhong@...el.com
Subject: [PATCH v3 09/22] kvm: x86: Enable dynamic XSAVE features at KVM_SET_CPUID2

Statically enable all xfeatures allowed by guest perm in
KVM_SET_CPUID2, with fpstate buffer sized accordingly. This avoids
run-time expansion in the emulation and restore path of XCR0 and
XFD MSR [1].

Change kvm_vcpu_after_set_cpuid() to return error given fpstate
reallocation may fail.

[1] https://lore.kernel.org/all/20211214024948.048572883@linutronix.de/

Suggested-by: Thomas Gleixner <tglx@...utronix.de>
Suggested-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Jing Liu <jing2.liu@...el.com>
---
 arch/x86/kvm/cpuid.c | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index a068373a7fbd..eb5a5070accb 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -204,10 +204,12 @@ void kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu)
 }
 EXPORT_SYMBOL_GPL(kvm_update_cpuid_runtime);
 
-static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
+static int kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 {
 	struct kvm_lapic *apic = vcpu->arch.apic;
 	struct kvm_cpuid_entry2 *best;
+	u64 xfeatures;
+	int r;
 
 	best = kvm_find_cpuid_entry(vcpu, 1, 0);
 	if (best && apic) {
@@ -222,9 +224,17 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 	best = kvm_find_cpuid_entry(vcpu, 0xD, 0);
 	if (!best)
 		vcpu->arch.guest_supported_xcr0 = 0;
-	else
-		vcpu->arch.guest_supported_xcr0 =
-			(best->eax | ((u64)best->edx << 32)) & supported_xcr0;
+	else {
+		xfeatures = best->eax | ((u64)best->edx << 32);
+
+		vcpu->arch.guest_supported_xcr0 = xfeatures & supported_xcr0;
+
+		if (xfeatures != vcpu->arch.guest_fpu.xfeatures) {
+			r = fpu_update_guest_perm_features(&vcpu->arch.guest_fpu);
+			if (r)
+				return r;
+		}
+	}
 
 	/*
 	 * Bits 127:0 of the allowed SECS.ATTRIBUTES (CPUID.0x12.0x1) enumerate
@@ -260,6 +270,8 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 	 * adjustments to the reserved GPA bits.
 	 */
 	kvm_mmu_after_set_cpuid(vcpu);
+
+	return 0;
 }
 
 int cpuid_query_maxphyaddr(struct kvm_vcpu *vcpu)
@@ -301,9 +313,7 @@ static int kvm_set_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2,
 
 	kvm_update_kvm_cpuid_base(vcpu);
 	kvm_update_cpuid_runtime(vcpu);
-	kvm_vcpu_after_set_cpuid(vcpu);
-
-	return 0;
+	return kvm_vcpu_after_set_cpuid(vcpu);
 }
 
 /* when an old userspace process fills a new kernel module */
-- 
2.27.0