KVM: x86/mmu: Consult max mapping level when zapping collapsible SPTEs

When zapping SPTEs in order to rebuild them as huge pages, use the new
helper that computes the max mapping level to detect whether or not a
SPTE should be zapped.  Doing so avoids zapping SPTEs that can't
possibly be rebuilt as huge pages, e.g. due to hardware constraints,
memslot alignment, etc...

This also avoids zapping SPTEs that are still large, e.g. if migration
was canceled before write-protected huge pages were shattered to enable
dirty logging.  Note, such pages are still write-protected at this time,
i.e. a page fault VM-Exit will still occur.  This will hopefully be
addressed in a future patch.

Sadly, TDP MMU loses its const on the memslot, but that's a pervasive
problem that's been around for quite some time.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210213005015.1651772-6-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 6 insertions, 5 deletions

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index e6f06eac11cb..4f2dfd59f9a2 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -5553,8 +5553,8 @@ restart:
 		 * mapping if the indirect sp has level = 1.
 		 */
 		if (sp->role.direct && !kvm_is_reserved_pfn(pfn) &&
-		    (kvm_is_zone_device_pfn(pfn) ||
-		     PageCompound(pfn_to_page(pfn)))) {
+		    sp->role.level < kvm_mmu_max_mapping_level(kvm, slot, sp->gfn,
+							       pfn, PG_LEVEL_NUM)) {
 			pte_list_remove(rmap_head, sptep);
 
 			if (kvm_available_flush_tlb_with_range())
@@ -5574,12 +5574,13 @@ void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm,
 				   const struct kvm_memory_slot *memslot)
 {
 	/* FIXME: const-ify all uses of struct kvm_memory_slot.  */
+	struct kvm_memory_slot *slot = (struct kvm_memory_slot *)memslot;
+
 	write_lock(&kvm->mmu_lock);
-	slot_handle_leaf(kvm, (struct kvm_memory_slot *)memslot,
-			 kvm_mmu_zap_collapsible_spte, true);
+	slot_handle_leaf(kvm, slot, kvm_mmu_zap_collapsible_spte, true);
 
 	if (is_tdp_mmu_enabled(kvm))
-		kvm_tdp_mmu_zap_collapsible_sptes(kvm, memslot);
+		kvm_tdp_mmu_zap_collapsible_sptes(kvm, slot);
 	write_unlock(&kvm->mmu_lock);
 }