[RFC PATCH 11/12] KVM: arm64: Split huge pages during KVM_CLEAR_DIRTY_LOG

[Ricardo Koller <ricarkol@google.com>]

This is the arm64 counterpart of commit cb00a70bd4b7 ("KVM: x86/mmu:
Split huge pages mapped by the TDP MMU during KVM_CLEAR_DIRTY_LOG"),
which has the benefit of splitting the cost of splitting a memslot
across multiple ioctls.

Split huge pages on the range specified using KVM_CLEAR_DIRTY_LOG.  And
do not split when enabling dirty logging if KVM_DIRTY_LOG_INITIALLY_SET
is set.

Signed-off-by: Ricardo Koller <ricarkol@google.com>
---
 arch/arm64/kvm/mmu.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 7881df411643..b8211d833cc1 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1076,8 +1076,8 @@ static void kvm_mmu_split_memory_region(struct kvm *kvm, int slot)
  * @mask:	The mask of pages at offset 'gfn_offset' in this memory
  *		slot to enable dirty logging on
  *
- * Writes protect selected pages to enable dirty logging for them. Caller must
- * acquire kvm->mmu_lock.
+ * Splits selected pages to PAGE_SIZE and then writes protect them to enable
+ * dirty logging for them. Caller must acquire kvm->mmu_lock.
  */
 void kvm_arch_mmu_enable_log_dirty_pt_masked(struct kvm *kvm,
 		struct kvm_memory_slot *slot,
@@ -1090,6 +1090,14 @@ void kvm_arch_mmu_enable_log_dirty_pt_masked(struct kvm *kvm,
 	lockdep_assert_held_write(&kvm->mmu_lock);
 
 	stage2_wp_range(&kvm->arch.mmu, start, end);
+
+	/*
+	 * If initially-all-set mode is not set, then huge-pages were already
+	 * split when enabling dirty logging: no need to do it again.
+	 */
+	if (kvm_dirty_log_manual_protect_and_init_set(kvm) &&
+	    READ_ONCE(eager_page_split))
+		kvm_mmu_split_huge_pages(kvm, start, end);
 }
 
 static void kvm_send_hwpoison_signal(unsigned long address, short lsb)
@@ -1474,10 +1482,11 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 	 */
 	if (fault_status == FSC_PERM && vma_pagesize == fault_granule)
 		ret = kvm_pgtable_stage2_relax_perms(pgt, fault_ipa, prot);
-	else
+	else {
 		ret = kvm_pgtable_stage2_map(pgt, fault_ipa, vma_pagesize,
 					     __pfn_to_phys(pfn), prot,
 					     memcache, KVM_PGTABLE_WALK_SHARED);
+	}
 
 	/* Mark the page dirty only if the fault is handled successfully */
 	if (writable && !ret) {
@@ -1887,7 +1896,9 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 		 * this when deleting, moving, disabling dirty logging, or
 		 * creating the memslot (a nop). Doing it for deletes makes
 		 * sure we don't leak memory, and there's no need to keep the
-		 * cache around for any of the other cases.
+		 * cache around for any of the other cases. Keeping the cache
+		 * is useful for succesive KVM_CLEAR_DIRTY_LOG calls, which is
+		 * not handled in this function.
 		 */
 		kvm_mmu_free_memory_cache(&kvm->arch.mmu.split_page_cache);
 	}
-- 
2.38.1.431.g37b22c650d-goog