KVM: x86/mmu: Check write tracking in all address spaces

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 <kimjw04271234@gmail.com>
Message-ID: <20260721103512.2136240-2-kimjw04271234@gmail.com>
[invert direction of the conditional. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/mmu/page_track.c b/arch/x86/kvm/mmu/page_track.c
index 1b17b12393a8cb2d8624d39a7b419433debe9516..7e8195a311bb028e2af2fa8e2420714886cb74ea 100644 (file)
--- a/arch/x86/kvm/mmu/page_track.c
+++ b/arch/x86/kvm/mmu/page_track.c
@@ -130,13 +130,23 @@ 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;
@@ -144,8 +154,18 @@ 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_MAX_NR_ADDRESS_SPACES > 2);
+
+       if (__kvm_gfn_is_write_tracked(slot, gfn))
+               return true;
+
+       if (kvm_arch_nr_memslot_as_ids(kvm) > 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