From: David Matlack dmatlack@google.com
[ Upstream commit 610265ea3da117db435868bd109f1861534a5634 ]
slot_handle_leaf is a misnomer because it only operates on 4K SPTEs whereas "leaf" is used to describe any valid terminal SPTE (4K or large page). Rename slot_handle_leaf to slot_handle_level_4k to avoid confusion.
Making this change makes it more obvious there is a benign discrepency between the legacy MMU and the TDP MMU when it comes to dirty logging. The legacy MMU only iterates through 4K SPTEs when zapping for collapsing and when clearing D-bits. The TDP MMU, on the other hand, iterates through SPTEs on all levels.
The TDP MMU behavior of zapping SPTEs at all levels is technically overkill for its current dirty logging implementation, which always demotes to 4k SPTES, but both the TDP MMU and legacy MMU zap if and only if the SPTE can be replaced by a larger page, i.e. will not spuriously zap 2m (or larger) SPTEs. Opportunistically add comments to explain this discrepency in the code.
Signed-off-by: David Matlack dmatlack@google.com Message-Id: 20211019162223.3935109-1-dmatlack@google.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/kvm/mmu/mmu.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 287fc1086db78..f2e74e8c1651a 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -5474,8 +5474,8 @@ slot_handle_level(struct kvm *kvm, const struct kvm_memory_slot *memslot, }
static __always_inline bool -slot_handle_leaf(struct kvm *kvm, const struct kvm_memory_slot *memslot, - slot_level_handler fn, bool flush_on_yield) +slot_handle_level_4k(struct kvm *kvm, const struct kvm_memory_slot *memslot, + slot_level_handler fn, bool flush_on_yield) { return slot_handle_level(kvm, memslot, fn, PG_LEVEL_4K, PG_LEVEL_4K, flush_on_yield); @@ -5859,7 +5859,12 @@ void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm,
if (kvm_memslots_have_rmaps(kvm)) { write_lock(&kvm->mmu_lock); - flush = slot_handle_leaf(kvm, slot, kvm_mmu_zap_collapsible_spte, true); + /* + * Zap only 4k SPTEs since the legacy MMU only supports dirty + * logging at a 4k granularity and never creates collapsible + * 2m SPTEs during dirty logging. + */ + flush = slot_handle_level_4k(kvm, slot, kvm_mmu_zap_collapsible_spte, true); if (flush) kvm_arch_flush_remote_tlbs_memslot(kvm, slot); write_unlock(&kvm->mmu_lock); @@ -5896,8 +5901,11 @@ void kvm_mmu_slot_leaf_clear_dirty(struct kvm *kvm,
if (kvm_memslots_have_rmaps(kvm)) { write_lock(&kvm->mmu_lock); - flush = slot_handle_leaf(kvm, memslot, __rmap_clear_dirty, - false); + /* + * Clear dirty bits only on 4k SPTEs since the legacy MMU only + * support dirty logging at a 4k granularity. + */ + flush = slot_handle_level_4k(kvm, memslot, __rmap_clear_dirty, false); write_unlock(&kvm->mmu_lock); }