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authorDr. David Alan Gilbert <dgilbert@redhat.com>2022-08-24 03:30:56 +0000
committerPaolo Bonzini <pbonzini@redhat.com>2022-09-22 17:04:19 -0400
commita1020a25e69755a8a1a37735d674b91d6f02939f (patch)
treef7cb4ddafd6f1c74fdada1dba7341ba023435e75 /arch
parentee519b3a2ae3027c341bce829ee8c51f4f494f5b (diff)
KVM: x86: Always enable legacy FP/SSE in allowed user XFEATURES
Allow FP and SSE state to be saved and restored via KVM_{G,SET}_XSAVE on XSAVE-capable hosts even if their bits are not exposed to the guest via XCR0. Failing to allow FP+SSE first showed up as a QEMU live migration failure, where migrating a VM from a pre-XSAVE host, e.g. Nehalem, to an XSAVE host failed due to KVM rejecting KVM_SET_XSAVE. However, the bug also causes problems even when migrating between XSAVE-capable hosts as KVM_GET_SAVE won't set any bits in user_xfeatures if XSAVE isn't exposed to the guest, i.e. KVM will fail to actually migrate FP+SSE. Because KVM_{G,S}ET_XSAVE are designed to allowing migrating between hosts with and without XSAVE, KVM_GET_XSAVE on a non-XSAVE (by way of fpu_copy_guest_fpstate_to_uabi()) always sets the FP+SSE bits in the header so that KVM_SET_XSAVE will work even if the new host supports XSAVE. Fixes: ad856280ddea ("x86/kvm/fpu: Limit guest user_xfeatures to supported bits of XCR0") bz: https://bugzilla.redhat.com/show_bug.cgi?id=2079311 Cc: stable@vger.kernel.org Cc: Leonardo Bras <leobras@redhat.com> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com> [sean: add comment, massage changelog] Signed-off-by: Sean Christopherson <seanjc@google.com> Message-Id: <20220824033057.3576315-3-seanjc@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/kvm/cpuid.c8
1 files changed, 7 insertions, 1 deletions
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 2e0f27ad736a..4c1c2c06e96b 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -329,7 +329,13 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
vcpu->arch.guest_supported_xcr0 =
cpuid_get_supported_xcr0(vcpu->arch.cpuid_entries, vcpu->arch.cpuid_nent);
- vcpu->arch.guest_fpu.fpstate->user_xfeatures = vcpu->arch.guest_supported_xcr0;
+ /*
+ * FP+SSE can always be saved/restored via KVM_{G,S}ET_XSAVE, even if
+ * XSAVE/XCRO are not exposed to the guest, and even if XSAVE isn't
+ * supported by the host.
+ */
+ vcpu->arch.guest_fpu.fpstate->user_xfeatures = vcpu->arch.guest_supported_xcr0 |
+ XFEATURE_MASK_FPSSE;
kvm_update_pv_runtime(vcpu);