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[6/7] KVM: x86/mmu: WARN if huge page recovery triggered during dirty logging

Message ID 20240805233114.4060019-7-dmatlack@google.com (mailing list archive)
State New, archived
Headers show
Series KVM: x86/mmu: Optimize TDP MMU huge page recovery during disable-dirty-log | expand

Commit Message

David Matlack Aug. 5, 2024, 11:31 p.m. UTC 
WARN and bail out of recover_huge_pages_range() if dirty logging is
enabled. KVM shouldn't be recovering huge pages during dirty logging
anyway, since KVM needs to track writes at 4KiB. However its not out of
the possibility that that changes in the future.

If KVM wants to recover huge pages during dirty logging,
make_huge_spte() must be updated to write-protect the new huge page
mapping. Otherwise, writes through the newly recovered huge page mapping
will not be tracked.

Note that this potential risk did not exist back when KVM zapped to
recover huge page mappings, since subsequent accesses would just be
faulted in at PG_LEVEL_4K if dirty logging was enabled.

Signed-off-by: David Matlack <dmatlack@google.com>
---
 arch/x86/kvm/mmu/tdp_mmu.c | 3 +++
 1 file changed, 3 insertions(+)
diff mbox series

Patch

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 9da319fd840e..07d5363c9db7 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1586,6 +1586,9 @@  static void recover_huge_pages_range(struct kvm *kvm,
 	bool flush = false;
 	u64 huge_spte;
 
+	if (WARN_ON_ONCE(kvm_slot_dirty_track_enabled(slot)))
+		return;
+
 	rcu_read_lock();
 
 	tdp_root_for_each_pte(iter, root, start, end) {