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| author | Dr. David Alan Gilbert <dgilbert@redhat.com> | 2022-08-24 03:30:56 +0000 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2022-09-22 17:04:19 -0400 |
| commit | a1020a25e69755a8a1a37735d674b91d6f02939f (patch) | |
| tree | f7cb4ddafd6f1c74fdada1dba7341ba023435e75 | |
| parent | ee519b3a2ae3027c341bce829ee8c51f4f494f5b (diff) | |
| download | linux-trace-a1020a25e69755a8a1a37735d674b91d6f02939f.tar.gz | |
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>
| -rw-r--r-- | arch/x86/kvm/cpuid.c | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index 2e0f27ad736a16..4c1c2c06e96bb2 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); |