From: Sean Christopherson seanjc@google.com
commit ee519b3a2ae3027c341bce829ee8c51f4f494f5b upstream.
Reinstate the per-vCPU guest_supported_xcr0 by partially reverting commit 988896bb6182; the implicit assessment that guest_supported_xcr0 is always the same as guest_fpu.fpstate->user_xfeatures was incorrect.
kvm_vcpu_after_set_cpuid() isn't the only place that sets user_xfeatures, as user_xfeatures is set to fpu_user_cfg.default_features when guest_fpu is allocated via fpu_alloc_guest_fpstate() => __fpstate_reset(). guest_supported_xcr0 on the other hand is zero-allocated. If userspace never invokes KVM_SET_CPUID2, supported XCR0 will be '0', whereas the allowed user XFEATURES will be non-zero.
Practically speaking, the edge case likely doesn't matter as no sane userspace will live migrate a VM without ever doing KVM_SET_CPUID2. The primary motivation is to prepare for KVM intentionally and explicitly setting bits in user_xfeatures that are not set in guest_supported_xcr0.
Because KVM_{G,S}ET_XSAVE can be used to svae/restore FP+SSE state even if the host doesn't support XSAVE, KVM needs to set the FP+SSE bits in user_xfeatures even if they're not allowed in XCR0, e.g. because XCR0 isn't exposed to the guest. At that point, the simplest fix is to track the two things separately (allowed save/restore vs. allowed XCR0).
Fixes: 988896bb6182 ("x86/kvm/fpu: Remove kvm_vcpu_arch.guest_supported_xcr0") Cc: stable@vger.kernel.org Cc: Leonardo Bras leobras@redhat.com Signed-off-by: Sean Christopherson seanjc@google.com Message-Id: 20220824033057.3576315-2-seanjc@google.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/include/asm/kvm_host.h | 1 + arch/x86/kvm/cpuid.c | 5 ++--- arch/x86/kvm/x86.c | 9 ++------- 3 files changed, 5 insertions(+), 10 deletions(-)
--- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -713,6 +713,7 @@ struct kvm_vcpu_arch { struct fpu_guest guest_fpu;
u64 xcr0; + u64 guest_supported_xcr0;
struct kvm_pio_request pio; void *pio_data; --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -283,7 +283,6 @@ static void kvm_vcpu_after_set_cpuid(str { struct kvm_lapic *apic = vcpu->arch.apic; struct kvm_cpuid_entry2 *best; - u64 guest_supported_xcr0;
best = kvm_find_cpuid_entry(vcpu, 1, 0); if (best && apic) { @@ -295,10 +294,10 @@ static void kvm_vcpu_after_set_cpuid(str kvm_apic_set_version(vcpu); }
- guest_supported_xcr0 = + vcpu->arch.guest_supported_xcr0 = cpuid_get_supported_xcr0(vcpu->arch.cpuid_entries, vcpu->arch.cpuid_nent);
- vcpu->arch.guest_fpu.fpstate->user_xfeatures = guest_supported_xcr0; + vcpu->arch.guest_fpu.fpstate->user_xfeatures = vcpu->arch.guest_supported_xcr0;
kvm_update_pv_runtime(vcpu);
--- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1025,15 +1025,10 @@ void kvm_load_host_xsave_state(struct kv } EXPORT_SYMBOL_GPL(kvm_load_host_xsave_state);
-static inline u64 kvm_guest_supported_xcr0(struct kvm_vcpu *vcpu) -{ - return vcpu->arch.guest_fpu.fpstate->user_xfeatures; -} - #ifdef CONFIG_X86_64 static inline u64 kvm_guest_supported_xfd(struct kvm_vcpu *vcpu) { - return kvm_guest_supported_xcr0(vcpu) & XFEATURE_MASK_USER_DYNAMIC; + return vcpu->arch.guest_supported_xcr0 & XFEATURE_MASK_USER_DYNAMIC; } #endif
@@ -1056,7 +1051,7 @@ static int __kvm_set_xcr(struct kvm_vcpu * saving. However, xcr0 bit 0 is always set, even if the * emulated CPU does not support XSAVE (see kvm_vcpu_reset()). */ - valid_bits = kvm_guest_supported_xcr0(vcpu) | XFEATURE_MASK_FP; + valid_bits = vcpu->arch.guest_supported_xcr0 | XFEATURE_MASK_FP; if (xcr0 & ~valid_bits) return 1;