Merge branch kvm-arm64/parallel-access-faults into kvmarm/next

* kvm-arm64/parallel-access-faults:
  : Parallel stage-2 access fault handling
  :
  : The parallel faults changes that went in to 6.2 covered most stage-2
  : aborts, with the exception of stage-2 access faults. Building on top of
  : the new infrastructure, this series adds support for handling access
  : faults (i.e. updating the access flag) in parallel.
  :
  : This is expected to provide a performance uplift for cores that do not
  : implement FEAT_HAFDBS, such as those from the fruit company.
  KVM: arm64: Condition HW AF updates on config option
  KVM: arm64: Handle access faults behind the read lock
  KVM: arm64: Don't serialize if the access flag isn't set
  KVM: arm64: Return EAGAIN for invalid PTE in attr walker
  KVM: arm64: Ignore EAGAIN for walks outside of a fault
  KVM: arm64: Use KVM's pte type/helpers in handle_access_fault()

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

arch/arm64/include/asm/kvm_pgtable.h

@@ -71,6 +71,11 @@ static inline kvm_pte_t kvm_phys_to_pte(u64 pa)
 	return pte;
 }
 
+static inline kvm_pfn_t kvm_pte_to_pfn(kvm_pte_t pte)
+{
+	return __phys_to_pfn(kvm_pte_to_phys(pte));
+}
+
 static inline u64 kvm_granule_shift(u32 level)
 {
 	/* Assumes KVM_PGTABLE_MAX_LEVELS is 4 */
@@ -188,12 +193,15 @@ typedef bool (*kvm_pgtable_force_pte_cb_t)(u64 addr, u64 end,
  *					children.
  * @KVM_PGTABLE_WALK_SHARED:		Indicates the page-tables may be shared
  *					with other software walkers.
+ * @KVM_PGTABLE_WALK_HANDLE_FAULT:	Indicates the page-table walk was
+ *					invoked from a fault handler.
  */
 enum kvm_pgtable_walk_flags {
 	KVM_PGTABLE_WALK_LEAF			= BIT(0),
 	KVM_PGTABLE_WALK_TABLE_PRE		= BIT(1),
 	KVM_PGTABLE_WALK_TABLE_POST		= BIT(2),
 	KVM_PGTABLE_WALK_SHARED			= BIT(3),
+	KVM_PGTABLE_WALK_HANDLE_FAULT		= BIT(4),
 };
 
 struct kvm_pgtable_visit_ctx {

arch/arm64/kvm/hyp/pgtable.c

@@ -168,6 +168,25 @@ static int kvm_pgtable_visitor_cb(struct kvm_pgtable_walk_data *data,
 	return walker->cb(ctx, visit);
 }
 
+static bool kvm_pgtable_walk_continue(const struct kvm_pgtable_walker *walker,
+				      int r)
+{
+	/*
+	 * Visitor callbacks return EAGAIN when the conditions that led to a
+	 * fault are no longer reflected in the page tables due to a race to
+	 * update a PTE. In the context of a fault handler this is interpreted
+	 * as a signal to retry guest execution.
+	 *
+	 * Ignore the return code altogether for walkers outside a fault handler
+	 * (e.g. write protecting a range of memory) and chug along with the
+	 * page table walk.
+	 */
+	if (r == -EAGAIN)
+		return !(walker->flags & KVM_PGTABLE_WALK_HANDLE_FAULT);
+
+	return !r;
+}
+
 static int __kvm_pgtable_walk(struct kvm_pgtable_walk_data *data,
 			      struct kvm_pgtable_mm_ops *mm_ops, kvm_pteref_t pgtable, u32 level);
 
@@ -200,7 +219,7 @@ static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data,
 		table = kvm_pte_table(ctx.old, level);
 	}
 
-	if (ret)
+	if (!kvm_pgtable_walk_continue(data->walker, ret))
 		goto out;
 
 	if (!table) {
@@ -211,13 +230,16 @@ static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data,
 
 	childp = (kvm_pteref_t)kvm_pte_follow(ctx.old, mm_ops);
 	ret = __kvm_pgtable_walk(data, mm_ops, childp, level + 1);
-	if (ret)
+	if (!kvm_pgtable_walk_continue(data->walker, ret))
 		goto out;
 
 	if (ctx.flags & KVM_PGTABLE_WALK_TABLE_POST)
 		ret = kvm_pgtable_visitor_cb(data, &ctx, KVM_PGTABLE_WALK_TABLE_POST);
 
 out:
+	if (kvm_pgtable_walk_continue(data->walker, ret))
+		return 0;
+
 	return ret;
 }
 
@@ -584,12 +606,14 @@ u64 kvm_get_vtcr(u64 mmfr0, u64 mmfr1, u32 phys_shift)
 		lvls = 2;
 	vtcr |= VTCR_EL2_LVLS_TO_SL0(lvls);
 
+#ifdef CONFIG_ARM64_HW_AFDBM
 	/*
 	 * Enable the Hardware Access Flag management, unconditionally
 	 * on all CPUs. The features is RES0 on CPUs without the support
 	 * and must be ignored by the CPUs.
 	 */
 	vtcr |= VTCR_EL2_HA;
+#endif /* CONFIG_ARM64_HW_AFDBM */
 
 	/* Set the vmid bits */
 	vtcr |= (get_vmid_bits(mmfr1) == 16) ?
@@ -1026,7 +1050,7 @@ static int stage2_attr_walker(const struct kvm_pgtable_visit_ctx *ctx,
 	struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
 
 	if (!kvm_pte_valid(ctx->old))
-		return 0;
+		return -EAGAIN;
 
 	data->level = ctx->level;
 	data->pte = pte;
@@ -1094,9 +1118,15 @@ int kvm_pgtable_stage2_wrprotect(struct kvm_pgtable *pgt, u64 addr, u64 size)
 kvm_pte_t kvm_pgtable_stage2_mkyoung(struct kvm_pgtable *pgt, u64 addr)
 {
 	kvm_pte_t pte = 0;
-	stage2_update_leaf_attrs(pgt, addr, 1, KVM_PTE_LEAF_ATTR_LO_S2_AF, 0,
-				 &pte, NULL, 0);
-	dsb(ishst);
+	int ret;
+
+	ret = stage2_update_leaf_attrs(pgt, addr, 1, KVM_PTE_LEAF_ATTR_LO_S2_AF, 0,
+				       &pte, NULL,
+				       KVM_PGTABLE_WALK_HANDLE_FAULT |
+				       KVM_PGTABLE_WALK_SHARED);
+	if (!ret)
+		dsb(ishst);
+
 	return pte;
 }
 
@@ -1141,6 +1171,7 @@ int kvm_pgtable_stage2_relax_perms(struct kvm_pgtable *pgt, u64 addr,
 		clr |= KVM_PTE_LEAF_ATTR_HI_S2_XN;
 
 	ret = stage2_update_leaf_attrs(pgt, addr, 1, set, clr, NULL, &level,
+				       KVM_PGTABLE_WALK_HANDLE_FAULT |
 				       KVM_PGTABLE_WALK_SHARED);
 	if (!ret)
 		kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, pgt->mmu, addr, level);

arch/arm64/kvm/mmu.c

@@ -1383,7 +1383,9 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 	else
 		ret = kvm_pgtable_stage2_map(pgt, fault_ipa, vma_pagesize,
 					     __pfn_to_phys(pfn), prot,
-					     memcache, KVM_PGTABLE_WALK_SHARED);
+					     memcache,
+					     KVM_PGTABLE_WALK_HANDLE_FAULT |
+					     KVM_PGTABLE_WALK_SHARED);
 
 	/* Mark the page dirty only if the fault is handled successfully */
 	if (writable && !ret) {
@@ -1401,20 +1403,18 @@ out_unlock:
 /* Resolve the access fault by making the page young again. */
 static void handle_access_fault(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa)
 {
-	pte_t pte;
-	kvm_pte_t kpte;
+	kvm_pte_t pte;
 	struct kvm_s2_mmu *mmu;
 
 	trace_kvm_access_fault(fault_ipa);
 
-	write_lock(&vcpu->kvm->mmu_lock);
+	read_lock(&vcpu->kvm->mmu_lock);
 	mmu = vcpu->arch.hw_mmu;
-	kpte = kvm_pgtable_stage2_mkyoung(mmu->pgt, fault_ipa);
-	write_unlock(&vcpu->kvm->mmu_lock);
+	pte = kvm_pgtable_stage2_mkyoung(mmu->pgt, fault_ipa);
+	read_unlock(&vcpu->kvm->mmu_lock);
 
-	pte = __pte(kpte);
-	if (pte_valid(pte))
-		kvm_set_pfn_accessed(pte_pfn(pte));
+	if (kvm_pte_valid(pte))
+		kvm_set_pfn_accessed(kvm_pte_to_pfn(pte));
 }
 
 /**