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Message-ID: <c337d280825c1e95d9181ab8aeb505a0b074c8d1.camel@redhat.com> Date: Wed, 23 Feb 2022 15:40:30 +0200 From: Maxim Levitsky <mlevitsk@...hat.com> To: Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org, kvm@...r.kernel.org Cc: seanjc@...gle.com, stable@...r.kernel.org Subject: Re: [PATCH v2 01/18] KVM: x86: host-initiated EFER.LME write affects the MMU On Thu, 2022-02-17 at 16:03 -0500, Paolo Bonzini wrote: > 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@...r.kernel.org > Signed-off-by: Paolo Bonzini <pbonzini@...hat.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; It makes sense. I am just curios, is there a report of failure due to this issue? I can imagine something like this breaking nested migration of 32 bit guests and such and/or smm and such. Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com> Best regards, Maxim Levitsky
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