Merge branch kvm-arm64/mmu/mte into kvmarm-master/next

KVM/arm64 support for MTE, courtesy of Steven Price.
It allows the guest to use memory tagging, and offers
a new userspace API to save/restore the tags.

* kvm-arm64/mmu/mte:
  KVM: arm64: Document MTE capability and ioctl
  KVM: arm64: Add ioctl to fetch/store tags in a guest
  KVM: arm64: Expose KVM_ARM_CAP_MTE
  KVM: arm64: Save/restore MTE registers
  KVM: arm64: Introduce MTE VM feature
  arm64: mte: Sync tags for pages where PTE is untagged

Signed-off-by: Marc Zyngier <maz@kernel.org>

1 files changed, 66 insertions, 0 deletions

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index bf389dfc885d..57292dc5ce35 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -853,6 +853,45 @@ static int get_vma_page_shift(struct vm_area_struct *vma, unsigned long hva)
 	return PAGE_SHIFT;
 }
 
+/*
+ * The page will be mapped in stage 2 as Normal Cacheable, so the VM will be
+ * able to see the page's tags and therefore they must be initialised first. If
+ * PG_mte_tagged is set, tags have already been initialised.
+ *
+ * The race in the test/set of the PG_mte_tagged flag is handled by:
+ * - preventing VM_SHARED mappings in a memslot with MTE preventing two VMs
+ *   racing to santise the same page
+ * - 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)
+{
+	unsigned long i, nr_pages = size >> PAGE_SHIFT;
+	struct page *page;
+
+	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;
+
+	for (i = 0; i < nr_pages; i++, page++) {
+		if (!test_bit(PG_mte_tagged, &page->flags)) {
+			mte_clear_page_tags(page_address(page));
+			set_bit(PG_mte_tagged, &page->flags);
+		}
+	}
+
+	return 0;
+}
+
 static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 			  struct kvm_memory_slot *memslot, unsigned long hva,
 			  unsigned long fault_status)
@@ -861,6 +900,7 @@ 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;
@@ -907,6 +947,8 @@ 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_PFNMAP);
+
 	switch (vma_shift) {
 #ifndef __PAGETABLE_PMD_FOLDED
 	case PUD_SHIFT:
@@ -1011,6 +1053,17 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 	if (vma_pagesize == PAGE_SIZE && !(force_pte || device))
 		vma_pagesize = transparent_hugepage_adjust(memslot, hva,
 							   &pfn, &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
+			ret = -EFAULT;
+		if (ret)
+			goto out_unlock;
+	}
+
 	if (writable)
 		prot |= KVM_PGTABLE_PROT_W;
 
@@ -1206,12 +1259,17 @@ 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)
+		return false;
+
 	/*
 	 * We've moved a page around, probably through CoW, so let's treat
 	 * it just like a translation fault and the map handler will clean
@@ -1414,6 +1472,14 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 		if (!vma)
 			break;
 
+		/*
+		 * VM_SHARED mappings are not allowed with MTE to avoid races
+		 * when updating the PG_mte_tagged page flag, see
+		 * sanitise_mte_tags for more details.
+		 */
+		if (kvm_has_mte(kvm) && vma->vm_flags & VM_SHARED)
+			return -EINVAL;
+
 		if (vma->vm_flags & VM_PFNMAP) {
 			/* IO region dirty page logging not allowed */
 			if (memslot->flags & KVM_MEM_LOG_DIRTY_PAGES) {