| Message ID | 20221110034122.9892-1-yan.y.zhao@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: x86/mmu: avoid accidentally go to shadow path for 0 count tdp root | expand |
On Thu, Nov 10, 2022, Yan Zhao wrote: > kvm mmu uses "if (is_tdp_mmu(vcpu->arch.mmu))" to choose between tdp mmu > and shadow path. > If a root is a tdp mmu page while its root_count is 0, it's not valid to > go to the shadow path. > > So, return true and add a warn on zero root count. > > Signed-off-by: Yan Zhao <yan.y.zhao@intel.com> > --- > arch/x86/kvm/mmu/tdp_mmu.h | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h > index c163f7cc23ca..58b4881654a9 100644 > --- a/arch/x86/kvm/mmu/tdp_mmu.h > +++ b/arch/x86/kvm/mmu/tdp_mmu.h > @@ -74,6 +74,7 @@ static inline bool is_tdp_mmu(struct kvm_mmu *mmu) > { > struct kvm_mmu_page *sp; > hpa_t hpa = mmu->root.hpa; > + bool is_tdp; > > if (WARN_ON(!VALID_PAGE(hpa))) > return false; > @@ -84,7 +85,10 @@ static inline bool is_tdp_mmu(struct kvm_mmu *mmu) > * pae_root page, not a shadow page. > */ > sp = to_shadow_page(hpa); > - return sp && is_tdp_mmu_page(sp) && sp->root_count; > + is_tdp = sp && is_tdp_mmu_page(sp); > + WARN_ON(is_tdp && !refcount_read(&sp->tdp_mmu_root_count)); > + > + return is_tdp; I have a series/patch that drops this code entirely, I would rather just go that route directly. https://lore.kernel.org/all/20221012181702.3663607-9-seanjc@google.com
On Thu, Nov 10, 2022 at 04:54:20PM +0000, Sean Christopherson wrote: > On Thu, Nov 10, 2022, Yan Zhao wrote: > > kvm mmu uses "if (is_tdp_mmu(vcpu->arch.mmu))" to choose between tdp mmu > > and shadow path. > > If a root is a tdp mmu page while its root_count is 0, it's not valid to > > go to the shadow path. > > > > So, return true and add a warn on zero root count. > > > > Signed-off-by: Yan Zhao <yan.y.zhao@intel.com> > > --- > > arch/x86/kvm/mmu/tdp_mmu.h | 6 +++++- > > 1 file changed, 5 insertions(+), 1 deletion(-) > > > > diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h > > index c163f7cc23ca..58b4881654a9 100644 > > --- a/arch/x86/kvm/mmu/tdp_mmu.h > > +++ b/arch/x86/kvm/mmu/tdp_mmu.h > > @@ -74,6 +74,7 @@ static inline bool is_tdp_mmu(struct kvm_mmu *mmu) > > { > > struct kvm_mmu_page *sp; > > hpa_t hpa = mmu->root.hpa; > > + bool is_tdp; > > > > if (WARN_ON(!VALID_PAGE(hpa))) > > return false; > > @@ -84,7 +85,10 @@ static inline bool is_tdp_mmu(struct kvm_mmu *mmu) > > * pae_root page, not a shadow page. > > */ > > sp = to_shadow_page(hpa); > > - return sp && is_tdp_mmu_page(sp) && sp->root_count; > > + is_tdp = sp && is_tdp_mmu_page(sp); > > + WARN_ON(is_tdp && !refcount_read(&sp->tdp_mmu_root_count)); > > + > > + return is_tdp; > > I have a series/patch that drops this code entirely, I would rather just go that > route directly. > > https://lore.kernel.org/all/20221012181702.3663607-9-seanjc@google.com Thanks for pointing me to this link. Yes, it's a much better fix! Thanks Yan
diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h index c163f7cc23ca..58b4881654a9 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.h +++ b/arch/x86/kvm/mmu/tdp_mmu.h @@ -74,6 +74,7 @@ static inline bool is_tdp_mmu(struct kvm_mmu *mmu) { struct kvm_mmu_page *sp; hpa_t hpa = mmu->root.hpa; + bool is_tdp; if (WARN_ON(!VALID_PAGE(hpa))) return false; @@ -84,7 +85,10 @@ static inline bool is_tdp_mmu(struct kvm_mmu *mmu) * pae_root page, not a shadow page. */ sp = to_shadow_page(hpa); - return sp && is_tdp_mmu_page(sp) && sp->root_count; + is_tdp = sp && is_tdp_mmu_page(sp); + WARN_ON(is_tdp && !refcount_read(&sp->tdp_mmu_root_count)); + + return is_tdp; } #else static inline int kvm_mmu_init_tdp_mmu(struct kvm *kvm) { return 0; }
kvm mmu uses "if (is_tdp_mmu(vcpu->arch.mmu))" to choose between tdp mmu and shadow path. If a root is a tdp mmu page while its root_count is 0, it's not valid to go to the shadow path. So, return true and add a warn on zero root count. Signed-off-by: Yan Zhao <yan.y.zhao@intel.com> --- arch/x86/kvm/mmu/tdp_mmu.h | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)