[PATCH v3 3/3] KVM: arm64: top up stage 2 memcache for dirty logging faults

[Bradley Morgan]

Dirty logging forces new stage 2 mappings down to page size, but
it does not always remove an existing block mapping before the next
fault. Eager splitting is best effort and is disabled by default.

A permission fault on such a block can still need a page table page
to install the smaller mapping. Top up the memcache for any permission
fault while dirty logging is active, not only for write faults.

The issue was discovered [1] by Sashiko.

Link: https://lore.kernel.org/all/59984F6D-06F2-4302-BDD7-92DF334E8FA0@xxxxxxxxx/T/#t [1]

Fixes: 6f745f1bb5bf ("KVM: arm64: Convert user_mem_abort() to generic page-table API")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Bradley Morgan <include@xxxxxxxxx>
---
 arch/arm64/kvm/mmu.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 3f57f6825a33..8911e319e6fa 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -2122,13 +2122,12 @@ static int user_mem_abort(const struct kvm_s2_fault_desc *s2fd)
 	 * Permission faults just need to update the existing leaf entry,
 	 * and so normally don't require allocations from the memcache. The
 	 * only exception to this is when dirty logging is enabled at runtime
-	 * and a write fault needs to collapse a block entry into a table. With
-	 * pKVM, they may still need a fresh mapping object if the fault turns
-	 * page entries into a block entry.
+	 * and a fault needs to collapse a block entry into a table. With pKVM,
+	 * they may still need a fresh mapping object if the fault turns page
+	 * entries into a block entry.
 	 */
 	memcache = get_mmu_memcache(s2fd->vcpu);
-	if (!perm_fault || (memslot_is_logging(s2fd->memslot) &&
-			    kvm_is_write_fault(s2fd->vcpu))) {
+	if (!perm_fault || memslot_is_logging(s2fd->memslot)) {
 		ret = topup_mmu_memcache(s2fd->vcpu, memcache);
 		if (ret)
 			return ret;
-- 
2.53.0