KVM: x86: Reinitialize context if host userspace toggles EFER.LME

BugLink: https://bugs.launchpad.net/bugs/1969110
commit d6174299365ddbbf491620c0b8c5ca1a6ef2eea5 upstream.

While the guest runs, EFER.LME cannot change unless CR0.PG is clear, and
therefore EFER.NX is the only bit that can affect the MMU role.  However,
set_efer accepts a host-initiated change to EFER.LME even with CR0.PG=1.
In that case, the MMU has to be reset.

Fixes: 11988499e62b ("KVM: x86: Skip EFER vs. guest CPUID checks for host-initiated writes")
Cc: stable@vger.kernel.org
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 48306afcac2a027163c6a8d10bd7a1d9d10efe37)
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>

diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index e9688a9f7b579d521caeee89017d9b557397c652..7bb165c2323348647507631ece9a2c6029799619 100644 (file)
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -49,6 +49,7 @@
                               X86_CR4_LA57)
 
 #define KVM_MMU_CR0_ROLE_BITS (X86_CR0_PG | X86_CR0_WP)
+#define KVM_MMU_EFER_ROLE_BITS (EFER_LME | EFER_NX)
 
 static __always_inline u64 rsvd_bits(int s, int e)
 {

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 52e4f6110aecf968721a5541b8b84931b2a24585..50ac0854575e552257ae4af777400116fe702f01 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1605,8 +1605,7 @@ static int set_efer(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
                return r;
        }
 
-       /* Update reserved bits */
-       if ((efer ^ old_efer) & EFER_NX)
+       if ((efer ^ old_efer) & KVM_MMU_EFER_ROLE_BITS)
                kvm_mmu_reset_context(vcpu);
 
        return 0;