5.15-stable review patch. If anyone has any objections, please let me know.
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From: Sean Christopherson seanjc@google.com
commit 4cdf351d3630a640ab6a05721ef055b9df62277f upstream.
In general, activating long mode involves setting the EFER_LME bit in the EFER register and then enabling the X86_CR0_PG bit in the CR0 register. At this point, the EFER_LMA bit will be set automatically by hardware.
In the case of SVM/SEV guests where writes to CR0 are intercepted, it's necessary for the host to set EFER_LMA on behalf of the guest since hardware does not see the actual CR0 write.
In the case of SEV-ES guests where writes to CR0 are trapped instead of intercepted, the hardware *does* see/record the write to CR0 before exiting and passing the value on to the host, so as part of enabling SEV-ES support commit f1c6366e3043 ("KVM: SVM: Add required changes to support intercepts under SEV-ES") dropped special handling of the EFER_LMA bit with the understanding that it would be set automatically.
However, since the guest never explicitly sets the EFER_LMA bit, the host never becomes aware that it has been set. This becomes problematic when userspace tries to get/set the EFER values via KVM_GET_SREGS/KVM_SET_SREGS, since the EFER contents tracked by the host will be missing the EFER_LMA bit, and when userspace attempts to pass the EFER value back via KVM_SET_SREGS it will fail a sanity check that asserts that EFER_LMA should always be set when X86_CR0_PG and EFER_LME are set.
Fix this by always inferring the value of EFER_LMA based on X86_CR0_PG and EFER_LME, regardless of whether or not SEV-ES is enabled.
Fixes: f1c6366e3043 ("KVM: SVM: Add required changes to support intercepts under SEV-ES") Reported-by: Peter Gonda pgonda@google.com Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson seanjc@google.com Message-Id: 20210507165947.2502412-2-seanjc@google.com [A two year old patch that was revived after we noticed the failure in KVM_SET_SREGS and a similar patch was posted by Michael Roth. This is Sean's patch, but with Michael's more complete commit message. - Paolo] Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kvm/svm/svm.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)
--- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -1750,15 +1750,17 @@ void svm_set_cr0(struct kvm_vcpu *vcpu, bool old_paging = is_paging(vcpu);
#ifdef CONFIG_X86_64 - if (vcpu->arch.efer & EFER_LME && !vcpu->arch.guest_state_protected) { + if (vcpu->arch.efer & EFER_LME) { if (!is_paging(vcpu) && (cr0 & X86_CR0_PG)) { vcpu->arch.efer |= EFER_LMA; - svm->vmcb->save.efer |= EFER_LMA | EFER_LME; + if (!vcpu->arch.guest_state_protected) + svm->vmcb->save.efer |= EFER_LMA | EFER_LME; }
if (is_paging(vcpu) && !(cr0 & X86_CR0_PG)) { vcpu->arch.efer &= ~EFER_LMA; - svm->vmcb->save.efer &= ~(EFER_LMA | EFER_LME); + if (!vcpu->arch.guest_state_protected) + svm->vmcb->save.efer &= ~(EFER_LMA | EFER_LME); } } #endif