KVM: arm64: Simplify the sanitise_mte_tags() logic

Currently sanitise_mte_tags() checks if it's an online page before
attempting to sanitise the tags. Such detection should be done in the
caller via the VM_MTE_ALLOWED vma flag. Since kvm_set_spte_gfn() does
not have the vma, leave the page unmapped if not already tagged. Tag
initialisation will be done on a subsequent access fault in
user_mem_abort().

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
[pcc@google.com: fix the page initializer]
Signed-off-by: Peter Collingbourne <pcc@google.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Peter Collingbourne <pcc@google.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221104011041.290951-4-pcc@google.com

arch/arm64/kvm/mmu.c

@@ -1091,32 +1091,21 @@ static int get_vma_page_shift(struct vm_area_struct *vma, unsigned long hva)
  * - mmap_lock protects between a VM faulting a page in and the VMM performing
  *   an mprotect() to add VM_MTE
  */
-static int sanitise_mte_tags(struct kvm *kvm, kvm_pfn_t pfn,
-			     unsigned long size)
+static void sanitise_mte_tags(struct kvm *kvm, kvm_pfn_t pfn,
+			      unsigned long size)
 {
 	unsigned long i, nr_pages = size >> PAGE_SHIFT;
-	struct page *page;
+	struct page *page = pfn_to_page(pfn);
 
 	if (!kvm_has_mte(kvm))
-		return 0;
-
-	/*
-	 * pfn_to_online_page() is used to reject ZONE_DEVICE pages
-	 * that may not support tags.
-	 */
-	page = pfn_to_online_page(pfn);
-
-	if (!page)
-		return -EFAULT;
+		return;
 
 	for (i = 0; i < nr_pages; i++, page++) {
 		if (!page_mte_tagged(page)) {
 			mte_clear_page_tags(page_address(page));
 			set_page_mte_tagged(page);
 		}
 	}
-
-	return 0;
 }
 
 static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
@@ -1127,7 +1116,6 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 	bool write_fault, writable, force_pte = false;
 	bool exec_fault;
 	bool device = false;
-	bool shared;
 	unsigned long mmu_seq;
 	struct kvm *kvm = vcpu->kvm;
 	struct kvm_mmu_memory_cache *memcache = &vcpu->arch.mmu_page_cache;
@@ -1177,8 +1165,6 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 		vma_shift = get_vma_page_shift(vma, hva);
 	}
 
-	shared = (vma->vm_flags & VM_SHARED);
-
 	switch (vma_shift) {
 #ifndef __PAGETABLE_PMD_FOLDED
 	case PUD_SHIFT:
@@ -1299,12 +1285,13 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 
 	if (fault_status != FSC_PERM && !device && kvm_has_mte(kvm)) {
 		/* Check the VMM hasn't introduced a new VM_SHARED VMA */
-		if (!shared)
-			ret = sanitise_mte_tags(kvm, pfn, vma_pagesize);
-		else
+		if ((vma->vm_flags & VM_MTE_ALLOWED) &&
+		    !(vma->vm_flags & VM_SHARED)) {
+			sanitise_mte_tags(kvm, pfn, vma_pagesize);
+		} else {
 			ret = -EFAULT;
-		if (ret)
 			goto out_unlock;
+		}
 	}
 
 	if (writable)
@@ -1526,15 +1513,18 @@ bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
 bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 {
 	kvm_pfn_t pfn = pte_pfn(range->pte);
-	int ret;
 
 	if (!kvm->arch.mmu.pgt)
 		return false;
 
 	WARN_ON(range->end - range->start != 1);
 
-	ret = sanitise_mte_tags(kvm, pfn, PAGE_SIZE);
-	if (ret)
+	/*
+	 * If the page isn't tagged, defer to user_mem_abort() for sanitising
+	 * the MTE tags. The S2 pte should have been unmapped by
+	 * mmu_notifier_invalidate_range_end().
+	 */
+	if (kvm_has_mte(kvm) && !page_mte_tagged(pfn_to_page(pfn)))
 		return false;
 
 	/*