Subject: [PATCH v2 06/30] KVM: arm64: Extract page table mapping in user_mem_abort()

From: Marc Zyngier <[email-masked]>
Date: Fri, 27 Mar 2026 11:35:54 +0000

From: Fuad Tabba <[email-masked]>

Extract the code responsible for locking the KVM MMU and mapping the PFN
into the stage-2 page tables into a new helper, kvm_s2_fault_map().

This helper manages the kvm_fault_lock, checks for MMU invalidation
retries, attempts to adjust for transparent huge pages (THP), handles
MTE sanitization if needed, and finally maps or relaxes permissions on
the stage-2 entries.

With this change, the main user_mem_abort() function is now a sequential
dispatcher that delegates to specialized helper functions.

Signed-off-by: Fuad Tabba <[email-masked]>
Signed-off-by: Marc Zyngier <[email-masked]>
---
 arch/arm64/kvm/mmu.c | 128 +++++++++++++++++++++++--------------------
 1 file changed, 68 insertions(+), 60 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index d1ffdce18631a..164f1160ea33d 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1892,68 +1892,13 @@ static int kvm_s2_fault_compute_prot(struct kvm_s2_fault *fault)
 	return 0;
 }
 
-static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
-			  struct kvm_s2_trans *nested,
-			  struct kvm_memory_slot *memslot, unsigned long hva,
-			  bool fault_is_perm)
+static int kvm_s2_fault_map(struct kvm_s2_fault *fault, void *memcache)
 {
-	int ret = 0;
-	struct kvm_s2_fault fault_data = {
-		.vcpu = vcpu,
-		.fault_ipa = fault_ipa,
-		.nested = nested,
-		.memslot = memslot,
-		.hva = hva,
-		.fault_is_perm = fault_is_perm,
-		.ipa = fault_ipa,
-		.logging_active = memslot_is_logging(memslot),
-		.force_pte = memslot_is_logging(memslot),
-		.s2_force_noncacheable = false,
-		.vfio_allow_any_uc = false,
-		.prot = KVM_PGTABLE_PROT_R,
-	};
-	struct kvm_s2_fault *fault = &fault_data;
-	struct kvm *kvm = vcpu->kvm;
-	void *memcache;
+	struct kvm *kvm = fault->vcpu->kvm;
 	struct kvm_pgtable *pgt;
+	int ret;
 	enum kvm_pgtable_walk_flags flags = KVM_PGTABLE_WALK_SHARED;
 
-	if (fault->fault_is_perm)
-		fault->fault_granule = kvm_vcpu_trap_get_perm_fault_granule(fault->vcpu);
-	fault->write_fault = kvm_is_write_fault(fault->vcpu);
-	fault->exec_fault = kvm_vcpu_trap_is_exec_fault(fault->vcpu);
-	VM_WARN_ON_ONCE(fault->write_fault && fault->exec_fault);
-
-	/*
-	 * 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.
-	 */
-	fault->topup_memcache = !fault->fault_is_perm ||
-				(fault->logging_active && fault->write_fault);
-	ret = prepare_mmu_memcache(fault->vcpu, fault->topup_memcache, &memcache);
-	if (ret)
-		return ret;
-
-	/*
-	 * Let's check if we will get back a huge page backed by hugetlbfs, or
-	 * get block mapping for device MMIO region.
-	 */
-	ret = kvm_s2_fault_pin_pfn(fault);
-	if (ret != 1)
-		return ret;
-
-	ret = 0;
-
-	ret = kvm_s2_fault_compute_prot(fault);
-	if (ret == 1) {
-		ret = 1; /* fault injected */
-		goto out_put_page;
-	}
-	if (ret)
-		goto out_put_page;
-
 	kvm_fault_lock(kvm);
 	pgt = fault->vcpu->arch.hw_mmu->pgt;
 	if (mmu_invalidate_retry(kvm, fault->mmu_seq)) {
@@ -2001,8 +1946,8 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 		 * PTE, which will be preserved.
 		 */
 		fault->prot &= ~KVM_NV_GUEST_MAP_SZ;
-		ret = KVM_PGT_FN(kvm_pgtable_stage2_relax_perms)(pgt, fault->fault_ipa, fault->prot,
-								 flags);
+		ret = KVM_PGT_FN(kvm_pgtable_stage2_relax_perms)(pgt, fault->fault_ipa,
+								 fault->prot, flags);
 	} else {
 		ret = KVM_PGT_FN(kvm_pgtable_stage2_map)(pgt, fault->fault_ipa, fault->vma_pagesize,
 							 __pfn_to_phys(fault->pfn), fault->prot,
@@ -2018,6 +1963,69 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 		mark_page_dirty_in_slot(kvm, fault->memslot, fault->gfn);
 
 	return ret != -EAGAIN ? ret : 0;
+}
+
+static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
+			  struct kvm_s2_trans *nested,
+			  struct kvm_memory_slot *memslot, unsigned long hva,
+			  bool fault_is_perm)
+{
+	int ret = 0;
+	struct kvm_s2_fault fault_data = {
+		.vcpu = vcpu,
+		.fault_ipa = fault_ipa,
+		.nested = nested,
+		.memslot = memslot,
+		.hva = hva,
+		.fault_is_perm = fault_is_perm,
+		.ipa = fault_ipa,
+		.logging_active = memslot_is_logging(memslot),
+		.force_pte = memslot_is_logging(memslot),
+		.s2_force_noncacheable = false,
+		.vfio_allow_any_uc = false,
+		.prot = KVM_PGTABLE_PROT_R,
+	};
+	struct kvm_s2_fault *fault = &fault_data;
+	void *memcache;
+
+	if (fault->fault_is_perm)
+		fault->fault_granule = kvm_vcpu_trap_get_perm_fault_granule(fault->vcpu);
+	fault->write_fault = kvm_is_write_fault(fault->vcpu);
+	fault->exec_fault = kvm_vcpu_trap_is_exec_fault(fault->vcpu);
+	VM_WARN_ON_ONCE(fault->write_fault && fault->exec_fault);
+
+	/*
+	 * 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.
+	 */
+	fault->topup_memcache = !fault->fault_is_perm ||
+				(fault->logging_active && fault->write_fault);
+	ret = prepare_mmu_memcache(fault->vcpu, fault->topup_memcache, &memcache);
+	if (ret)
+		return ret;
+
+	/*
+	 * Let's check if we will get back a huge page backed by hugetlbfs, or
+	 * get block mapping for device MMIO region.
+	 */
+	ret = kvm_s2_fault_pin_pfn(fault);
+	if (ret != 1)
+		return ret;
+
+	ret = 0;
+
+	ret = kvm_s2_fault_compute_prot(fault);
+	if (ret == 1) {
+		ret = 1; /* fault injected */
+		goto out_put_page;
+	}
+	if (ret)
+		goto out_put_page;
+
+	ret = kvm_s2_fault_map(fault, memcache);
+	return ret;
 
 out_put_page:
 	kvm_release_page_unused(fault->page);
-- 
2.47.3