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Mon, 09 Mar 2026 07:23:26 -0700 (PDT) Date: Mon, 9 Mar 2026 07:23:25 -0700 In-Reply-To: <20260309083844.217215-1-pcj3195161583@163.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260309083844.217215-1-pcj3195161583@163.com> Message-ID: Subject: Re: [PATCH] KVM: x86/tdp_mmu: Fix base gfn check when zapping private huge SPTE From: Sean Christopherson To: pcjer Cc: kvm@vger.kernel.org, pbonzini@redhat.com, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="us-ascii" On Mon, Mar 09, 2026, pcjer wrote: > Signed-off-by: pcjer > --- > arch/x86/kvm/mmu/tdp_mmu.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c > index 1266d5452..8482a85d6 100644 > --- a/arch/x86/kvm/mmu/tdp_mmu.c > +++ b/arch/x86/kvm/mmu/tdp_mmu.c > @@ -1025,8 +1025,8 @@ static bool tdp_mmu_zap_leafs(struct kvm *kvm, struct kvm_mmu_page *root, > > slot = gfn_to_memslot(kvm, gfn); > if (kvm_hugepage_test_mixed(slot, gfn, iter.level) || > - (gfn & mask) < start || > - end < (gfn & mask) + KVM_PAGES_PER_HPAGE(iter.level)) { > + (gfn & ~mask) < start || > + end < (gfn & ~mask) + KVM_PAGES_PER_HPAGE(iter.level)) { Somewhat to my surprise, this does indeed look like a legitimate fix, ignoring that the code in question was never merged and was lasted posted 2+ years ago[*] (and has long since been replaced). The bug likely went unnoticed during development because "(gfn & mask) < start" would almost always be true (mask == 511 for a 2MiB page). Though mask should really just be inverted from the get go in this code + if (is_private && kvm_gfn_shared_mask(kvm) && + is_large_pte(iter.old_spte)) { + gfn_t gfn = iter.gfn & ~kvm_gfn_shared_mask(kvm); + gfn_t mask = KVM_PAGES_PER_HPAGE(iter.level) - 1; + + struct kvm_memory_slot *slot; + struct kvm_mmu_page *sp; + [*] https://lore.kernel.org/all/c656573ccc68e212416d323d35f884bff25e6e2d.1708933624.git.isaku.yamahata@intel.com