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Wed, 26 Aug 2026 13:17:13 -0700 (PDT) Received: from localhost.localdomain ([2603:8001:5f01:8bab:957:eb3d:7323:2ed]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-3283d60b59dsm11179738eec.3.2026.08.26.13.17.12 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Wed, 26 Aug 2026 13:17:13 -0700 (PDT) From: Artem Dinaburg To: stable@vger.kernel.org Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, seanjc@google.com, pbonzini@redhat.com, kimjw04271234@gmail.com, Artem Dinaburg Subject: [PATCH 6.6.y 1/2] KVM: x86/mmu: Check write tracking in all address spaces Date: Wed, 26 Aug 2026 16:16:54 -0400 Message-ID: <20260826201655.9198-2-artem@trailofbits.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260826201655.9198-1-artem@trailofbits.com> References: <20260826201655.9198-1-artem@trailofbits.com> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Jinu Kim commit 0f38453cdb2e17566ccb7c0f3dabd5bd21caca26 upstream. kvm_gfn_is_write_tracked() checks only the supplied memslot, but page tracking is per-address-space and shadow pages are shared across all address spaces. With SMM, a GFN can therefore be write-tracked in one address space and appear untracked through the other. Check the supplied slot first, then the slot for the other address space. This ensures all callers honor write tracking regardless of the active address space. In particular, it prevents mmu_try_to_unsync_pages() from marking an upper-level shadow page unsync and eventually triggering the BUG in pte_list_remove(). Fixes: 699023e23965 ("KVM: x86: add SMM to the MMU role, support SMRAM address space") Assisted-by: Codex:GPT-5 Signed-off-by: Jinu Kim Message-ID: <20260721103512.2136240-2-kimjw04271234@gmail.com> [invert direction of the conditional. - Paolo] Signed-off-by: Paolo Bonzini [ artem: adapt to 6.6, which has neither KVM_MAX_NR_ADDRESS_SPACES nor kvm_arch_nr_memslot_as_ids(); use KVM_ADDRESS_SPACE_NUM instead. That macro is CONFIG_KVM_SMM-conditional in 6.6, so the guard on KVM_ADDRESS_SPACE_NUM > 1 around the peer-slot lookup is retained ] Signed-off-by: Artem Dinaburg --- Target tree: linux-6.6.y (stable). Verified: applies to v6.6.153; arch/x86/kvm/mmu/page_track.o builds clean with CONFIG_KVM_SMM=y and with CONFIG_KVM_SMM=n. arch/x86/kvm/mmu/page_track.c | 32 ++++++++++++++++++++++++++------ 1 file changed, 26 insertions(+), 6 deletions(-) diff --git a/arch/x86/kvm/mmu/page_track.c b/arch/x86/kvm/mmu/page_track.c index c87da11f3a04..2615074a4bff 100644 --- a/arch/x86/kvm/mmu/page_track.c +++ b/arch/x86/kvm/mmu/page_track.c @@ -117,13 +117,23 @@ void __kvm_write_track_remove_gfn(struct kvm *kvm, kvm_mmu_gfn_allow_lpage(slot, gfn); } -/* - * check if the corresponding access on the specified guest page is tracked. - */ +static bool __kvm_gfn_is_write_tracked(const struct kvm_memory_slot *slot, + gfn_t gfn) +{ + int index; + + if (!slot) + return false; + + index = gfn_to_index(gfn, slot->base_gfn, PG_LEVEL_4K); + return !!READ_ONCE(slot->arch.gfn_write_track[index]); +} + +/* check if write access is tracked on the specified guest page. */ bool kvm_gfn_is_write_tracked(struct kvm *kvm, const struct kvm_memory_slot *slot, gfn_t gfn) { - int index; + const struct kvm_memory_slot *other_slot; if (!slot) return false; @@ -131,8 +141,18 @@ bool kvm_gfn_is_write_tracked(struct kvm *kvm, if (!kvm_page_track_write_tracking_enabled(kvm)) return false; - index = gfn_to_index(gfn, slot->base_gfn, PG_LEVEL_4K); - return !!READ_ONCE(slot->arch.gfn_write_track[index]); + BUILD_BUG_ON(KVM_ADDRESS_SPACE_NUM > 2); + + if (__kvm_gfn_is_write_tracked(slot, gfn)) + return true; + + if (KVM_ADDRESS_SPACE_NUM > 1) { + other_slot = __gfn_to_memslot(__kvm_memslots(kvm, slot->as_id ^ 1), gfn); + if (__kvm_gfn_is_write_tracked(other_slot, gfn)) + return true; + } + + return false; } #ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING -- 2.43.0