From 56fd1fc526e6413781a6980aa13ed9db104cbfea Mon Sep 17 00:00:00 2001 From: Bradley Morgan Date: Fri, 17 Jul 2026 14:03:13 +0100 Subject: [PATCH] KVM: arm64: Top up stage-2 memcache for dirty logging faults Dirty logging forces new stage-2 mappings to page size but does not always split an existing block first (eager splitting is best effort and off by default). A non-write permission fault on such a block, an instruction fetch, still needs a page-table page to split it, but the top-up is gated on write faults. With the cache empty, kvm_mmu_memory_cache_alloc() hits its guest-triggerable WARN_ON(!nobjs) and falls back to a GFP_ATOMIC allocation under mmu_lock, with a BUG_ON() if that fails. Top up the memcache for any permission fault while dirty logging is active. Fixes: 6f745f1bb5bf ("KVM: arm64: Convert user_mem_abort() to generic page-table API") Link: https://lore.kernel.org/all/20260623165634.699011F000E9@smtp.kernel.org/ Signed-off-by: Bradley Morgan [tabba: reword the commit message for the generic, non-pKVM failure mode] Signed-off-by: Fuad Tabba Tested-by: Bradley Morgan # On pixel 7, Android 17 CP2A.260705.006 Test: Bradley Morgan # On QEMU arm64 host Link: https://patch.msgid.link/20260717130317.1953574-4-fuad.tabba@linux.dev Signed-off-by: Oliver Upton --- arch/arm64/kvm/mmu.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c index 4d7c9bdcef00..74e7e7f7564c 100644 --- a/arch/arm64/kvm/mmu.c +++ b/arch/arm64/kvm/mmu.c @@ -2113,14 +2113,13 @@ 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. + * and a fault needs to collapse a block entry into a table. * Under pKVM a permission fault can also collapse pages into a block, * which needs a fresh mapping object, and the hypervisor requires the * min-pages memcache even when the install allocates nothing. */ 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) || is_protected_kvm_enabled()) { ret = topup_mmu_memcache(s2fd->vcpu, memcache); if (ret)