On Wed, Dec 22, 2021, Jing Liu wrote:
Statically enable all xfeatures allowed by guest perm in
Statically isn't the right word. It's not dymanic with respect to running the vCPU, but it's certainly not static. I think you can just omit "Statically" entirely.
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;
IMO, this should be done and check before "committing" state, otherwise KVM will set the vCPU's CPUID info and update a variety of state, but then tell userspace that it failed. The -EPERM case in particular falls squarely into the "check" category.