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Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ] > > Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider: > - [High] kvm: x86/mmu: L2 GFN type confusion and missed PML logs for L2 page tables > -- > > commit 39018b0fb43ef6b337e5d8b61b880163828654c8 > Author: Nikunj A Dadhania > > KVM: x86/mmu: Log dirty GPAs only for the nested GPA walk > > This patch gates PML logging on the walk being the nested GPA walk, assuming > only that walk yields an L2 GPA. No functional change is intended as the EPT > template only backs the nested GPA walk. > >> diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h >> index 8e350095508c5..043d0ec02b272 100644 >> --- a/arch/x86/kvm/mmu/paging_tmpl.h >> +++ b/arch/x86/kvm/mmu/paging_tmpl.h >> @@ -235,7 +235,9 @@ static int FNAME(update_accessed_dirty_bits)(struct kvm_vcpu *vcpu, >> !(pte & PT_GUEST_DIRTY_MASK)) { >> trace_kvm_mmu_set_dirty_bit(table_gfn, index, sizeof(pte)); >> #if PTTYPE == PTTYPE_EPT >> - if (kvm_nested_call(write_log_dirty)(vcpu, addr)) >> + /* Only the nested GPA walk yields an L2 GPA to log. */ >> + if (w == &vcpu->arch.ngpa_walk && >> + kvm_nested_call(write_log_dirty)(vcpu, addr)) > > [Severity: High] > Does this change miss PML logs for L2 page table modifications that occur > during an L2 gva_walk? No, those are logged, just not from the gva_walk. Walking L2's page tables translates each page-table page through the nested walk, as a write: walk_addr_generic(w = gva_walk) nested_access = (have_ad ? PFERR_WRITE_MASK : 0) | PFERR_USER_MASK; kvm_translate_gpa(gva_walk, gfn_to_gpa(table_gfn), nested_access | ...) svm_translate_nested_gpa() /* switches w to ngpa_walk */ walk_addr_generic(w = ngpa_walk) /* write_fault is set */ update_accessed_dirty_bits() write_log_dirty(vcpu, addr) /* L2 GPA of the page table */ Logging from the gva_walk would be wrong rather than extra: 'addr' there is an L2 GVA, not a GPA. > > When KVM emulates setting A/D bits in an L2 page table (during an L2 > gva_walk), it is writing to an L2 GPA. Hardware logs page table updates > to the PML buffer, so it seems KVM must do the same. > > By ignoring gva_walk, does this fail to log L2 page table modifications > to L1's PML buffer, breaking L1's dirty page tracking? Regards, Nikunj