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Subject[PATCH v3 09/22] kvm: x86: Enable dynamic XSAVE features at KVM_SET_CPUID2
Date
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@linutronix.de>
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Jing Liu <jing2.liu@intel.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
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