KVM: arm64: Add kvm_pgtable_stage2_find_range()

Since the host stage 2 will be identity mapped, and since it will own
most of memory, it would preferable for performance to try and use large
block mappings whenever that is possible. To ease this, introduce a new
helper in the KVM page-table code which allows to search for large
ranges of available IPA space. This will be used in the host memory
abort path to greedily idmap large portion of the PA space.
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210319100146.1149909-32-qperret@google.com

arch/arm64/include/asm/kvm_pgtable.h

@@ -94,6 +94,16 @@ enum kvm_pgtable_prot {
 #define PAGE_HYP_RO		(KVM_PGTABLE_PROT_R)
 #define PAGE_HYP_DEVICE		(PAGE_HYP | KVM_PGTABLE_PROT_DEVICE)
 
+/**
+ * struct kvm_mem_range - Range of Intermediate Physical Addresses
+ * @start:	Start of the range.
+ * @end:	End of the range.
+ */
+struct kvm_mem_range {
+	u64 start;
+	u64 end;
+};
+
 /**
  * enum kvm_pgtable_walk_flags - Flags to control a depth-first page-table walk.
  * @KVM_PGTABLE_WALK_LEAF:		Visit leaf entries, including invalid
@@ -397,4 +407,23 @@ int kvm_pgtable_stage2_flush(struct kvm_pgtable *pgt, u64 addr, u64 size);
 int kvm_pgtable_walk(struct kvm_pgtable *pgt, u64 addr, u64 size,
 		     struct kvm_pgtable_walker *walker);
 
+/**
+ * kvm_pgtable_stage2_find_range() - Find a range of Intermediate Physical
+ *				     Addresses with compatible permission
+ *				     attributes.
+ * @pgt:	Page-table structure initialised by kvm_pgtable_stage2_init().
+ * @addr:	Address that must be covered by the range.
+ * @prot:	Protection attributes that the range must be compatible with.
+ * @range:	Range structure used to limit the search space at call time and
+ *		that will hold the result.
+ *
+ * The offset of @addr within a page is ignored. An IPA is compatible with @prot
+ * iff its corresponding stage-2 page-table entry has default ownership and, if
+ * valid, is mapped with protection attributes identical to @prot.
+ *
+ * Return: 0 on success, negative error code on failure.
+ */
+int kvm_pgtable_stage2_find_range(struct kvm_pgtable *pgt, u64 addr,
+				  enum kvm_pgtable_prot prot,
+				  struct kvm_mem_range *range);
 #endif	/* __ARM64_KVM_PGTABLE_H__ */

arch/arm64/kvm/hyp/pgtable.c

@@ -48,6 +48,8 @@
 					 KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W | \
 					 KVM_PTE_LEAF_ATTR_HI_S2_XN)
 
+#define KVM_PTE_LEAF_ATTR_S2_IGNORED	GENMASK(58, 55)
+
 #define KVM_INVALID_PTE_OWNER_MASK	GENMASK(63, 56)
 #define KVM_MAX_OWNER_ID		1
 
@@ -77,15 +79,20 @@ static bool kvm_phys_is_valid(u64 phys)
 	return phys < BIT(id_aa64mmfr0_parange_to_phys_shift(ID_AA64MMFR0_PARANGE_MAX));
 }
 
-static bool kvm_block_mapping_supported(u64 addr, u64 end, u64 phys, u32 level)
+static bool kvm_level_supports_block_mapping(u32 level)
 {
-	u64 granule = kvm_granule_size(level);
-
 	/*
 	 * Reject invalid block mappings and don't bother with 4TB mappings for
 	 * 52-bit PAs.
 	 */
-	if (level == 0 || (PAGE_SIZE != SZ_4K && level == 1))
+	return !(level == 0 || (PAGE_SIZE != SZ_4K && level == 1));
+}
+
+static bool kvm_block_mapping_supported(u64 addr, u64 end, u64 phys, u32 level)
+{
+	u64 granule = kvm_granule_size(level);
+
+	if (!kvm_level_supports_block_mapping(level))
 		return false;
 
 	if (granule > (end - addr))
@@ -1053,3 +1060,77 @@ void kvm_pgtable_stage2_destroy(struct kvm_pgtable *pgt)
 	pgt->mm_ops->free_pages_exact(pgt->pgd, pgd_sz);
 	pgt->pgd = NULL;
 }
+
+#define KVM_PTE_LEAF_S2_COMPAT_MASK	(KVM_PTE_LEAF_ATTR_S2_PERMS | \
+					 KVM_PTE_LEAF_ATTR_LO_S2_MEMATTR | \
+					 KVM_PTE_LEAF_ATTR_S2_IGNORED)
+
+static int stage2_check_permission_walker(u64 addr, u64 end, u32 level,
+					  kvm_pte_t *ptep,
+					  enum kvm_pgtable_walk_flags flag,
+					  void * const arg)
+{
+	kvm_pte_t old_attr, pte = *ptep, *new_attr = arg;
+
+	/*
+	 * Compatible mappings are either invalid and owned by the page-table
+	 * owner (whose id is 0), or valid with matching permission attributes.
+	 */
+	if (kvm_pte_valid(pte)) {
+		old_attr = pte & KVM_PTE_LEAF_S2_COMPAT_MASK;
+		if (old_attr != *new_attr)
+			return -EEXIST;
+	} else if (pte) {
+		return -EEXIST;
+	}
+
+	return 0;
+}
+
+int kvm_pgtable_stage2_find_range(struct kvm_pgtable *pgt, u64 addr,
+				  enum kvm_pgtable_prot prot,
+				  struct kvm_mem_range *range)
+{
+	kvm_pte_t attr;
+	struct kvm_pgtable_walker check_perm_walker = {
+		.cb		= stage2_check_permission_walker,
+		.flags		= KVM_PGTABLE_WALK_LEAF,
+		.arg		= &attr,
+	};
+	u64 granule, start, end;
+	u32 level;
+	int ret;
+
+	ret = stage2_set_prot_attr(prot, &attr);
+	if (ret)
+		return ret;
+	attr &= KVM_PTE_LEAF_S2_COMPAT_MASK;
+
+	for (level = pgt->start_level; level < KVM_PGTABLE_MAX_LEVELS; level++) {
+		granule = kvm_granule_size(level);
+		start = ALIGN_DOWN(addr, granule);
+		end = start + granule;
+
+		if (!kvm_level_supports_block_mapping(level))
+			continue;
+
+		if (start < range->start || range->end < end)
+			continue;
+
+		/*
+		 * Check the presence of existing mappings with incompatible
+		 * permissions within the current block range, and try one level
+		 * deeper if one is found.
+		 */
+		ret = kvm_pgtable_walk(pgt, start, granule, &check_perm_walker);
+		if (ret != -EEXIST)
+			break;
+	}
+
+	if (!ret) {
+		range->start = start;
+		range->end = end;
+	}
+
+	return ret;
+}