[PATCH 5.16 0857/1017] KVM: x86: Reinitialize context if host userspace toggles EFER.LME

Greg Kroah-Hartman
2022-04-05T13:41:59Z

From: Paolo Bonzini <pbonzini@redhat.com>

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>
---
arch/x86/kvm/mmu.h | 1 +
arch/x86/kvm/x86.c | 3 +--
2 files changed, 2 insertions(+), 2 deletions(-)

--- 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)
{
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1614,8 +1614,7 @@ static int set_efer(struct kvm_vcpu *vcp
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;