Messages in this thread | | | Date | Thu, 4 Aug 2022 18:08:22 +0100 | From | "Dr. David Alan Gilbert" <> | Subject | Re: [PATCH] KVM: x86: revalidate steal time cache if MSR value changes |
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* Vitaly Kuznetsov (vkuznets@redhat.com) wrote: > Paolo Bonzini <pbonzini@redhat.com> writes: > > > Commit 7e2175ebd695 ("KVM: x86: Fix recording of guest steal time > > / preempted status", 2021-11-11) open coded the previous call to > > kvm_map_gfn, but in doing so it dropped the comparison between the cached > > guest physical address and the one in the MSR. This cause an incorrect > > cache hit if the guest modifies the steal time address while the memslots > > remain the same. This can happen with kexec, in which case the steal > > time data is written at the address used by the old kernel instead of > > the old one. > > > > While at it, rename the variable from gfn to gpa since it is a plain > > physical address and not a right-shifted one. > > > > Reported-by: Dave Young <ruyang@redhat.com> > > Reported-by: Xiaoying Yan <yiyan@redhat.com> > > Analyzed-by: Dr. David Alan Gilbert <dgilbert@redhat.com> > > Cc: David Woodhouse <dwmw@amazon.co.uk> > > Cc: stable@vger.kernel.org > > Fixes: 7e2175ebd695 ("KVM: x86: Fix recording of guest steal time / preempted status") > > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> > > --- > > arch/x86/kvm/x86.c | 6 +++--- > > 1 file changed, 3 insertions(+), 3 deletions(-) > > > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > > index e5fa335a4ea7..36dcf18b04bf 100644 > > --- a/arch/x86/kvm/x86.c > > +++ b/arch/x86/kvm/x86.c > > @@ -3380,6 +3380,7 @@ static void record_steal_time(struct kvm_vcpu *vcpu) > > struct gfn_to_hva_cache *ghc = &vcpu->arch.st.cache; > > struct kvm_steal_time __user *st; > > struct kvm_memslots *slots; > > + gpa_t gpa = vcpu->arch.st.msr_val & KVM_STEAL_VALID_BITS; > > u64 steal; > > u32 version; > > > > @@ -3397,13 +3398,12 @@ static void record_steal_time(struct kvm_vcpu *vcpu) > > slots = kvm_memslots(vcpu->kvm); > > > > if (unlikely(slots->generation != ghc->generation || > > + gpa != ghc->gpa || > > kvm_is_error_hva(ghc->hva) || !ghc->memslot)) { > > - gfn_t gfn = vcpu->arch.st.msr_val & KVM_STEAL_VALID_BITS; > > - > > /* We rely on the fact that it fits in a single page. */ > > BUILD_BUG_ON((sizeof(*st) - 1) & KVM_STEAL_VALID_BITS); > > > > - if (kvm_gfn_to_hva_cache_init(vcpu->kvm, ghc, gfn, sizeof(*st)) || > > + if (kvm_gfn_to_hva_cache_init(vcpu->kvm, ghc, gpa, sizeof(*st)) || > > (It would be nice to somehow get at least a warning when 'gfn_t' is used > instead of 'gpa_t' and vice versa)
Can't sparse be taught to do that?
Dave
> > kvm_is_error_hva(ghc->hva) || !ghc->memslot) > > return; > > } > > Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com> > > -- > Vitaly > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
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