[PATCH v2 01/18] KVM: x86: host-initiated EFER.LME write affects the MMU

Paolo Bonzini
2022-02-17T21:03:54Z

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
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/mmu.h | 1 +
arch/x86/kvm/x86.c | 2 +-
2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 51faa2c76ca5..a5a50cfeffff 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -48,6 +48,7 @@
X86_CR4_SMEP | X86_CR4_SMAP | X86_CR4_PKE)

#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 d3da64106685..99a58c25f5c2 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1647,7 +1647,7 @@ static int set_efer(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
}

/* 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;
--
2.31.1