linux-kernel - [PATCH v4 04/21] KVM: arm64: Introduce helper to retrieve a PTE and its level

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Message-Id: <20210809152448.1810400-5-qperret@google.com>
Date:   Mon,  9 Aug 2021 16:24:31 +0100
From:   Quentin Perret <qperret@...gle.com>
To:     maz@...nel.org, james.morse@....com, alexandru.elisei@....com,
        suzuki.poulose@....com, catalin.marinas@....com, will@...nel.org
Cc:     linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, ardb@...nel.org, qwandor@...gle.com,
        tabba@...gle.com, dbrazdil@...gle.com, kernel-team@...roid.com,
        qperret@...gle.com
Subject: [PATCH v4 04/21] KVM: arm64: Introduce helper to retrieve a PTE and
 its level

From: Marc Zyngier <maz@...nel.org>

It is becoming a common need to fetch the PTE for a given address
together with its level. Add such a helper.

Signed-off-by: Marc Zyngier <maz@...nel.org>
Signed-off-by: Quentin Perret <qperret@...gle.com>
---
 arch/arm64/include/asm/kvm_pgtable.h | 19 ++++++++++++++
 arch/arm64/kvm/hyp/pgtable.c         | 39 ++++++++++++++++++++++++++++
 2 files changed, 58 insertions(+)

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index f004c0115d89..082b9d65f40b 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -432,6 +432,25 @@ 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_get_leaf() - Walk a page-table and retrieve the leaf entry
+ *			    with its level.
+ * @pgt:	Page-table structure initialised by kvm_pgtable_*_init().
+ * @addr:	Input address for the start of the walk.
+ * @ptep:	Pointer to storage for the retrieved PTE.
+ * @level:	Pointer to storage for the level of the retrieved PTE.
+ *
+ * The offset of @addr within a page is ignored.
+ *
+ * The walker will walk the page-table entries corresponding to the input
+ * address specified, retrieving the leaf corresponding to this address.
+ * Invalid entries are treated as leaf entries.
+ *
+ * Return: 0 on success, negative error code on failure.
+ */
+int kvm_pgtable_get_leaf(struct kvm_pgtable *pgt, u64 addr,
+			 kvm_pte_t *ptep, u32 *level);
+
 /**
  * kvm_pgtable_stage2_find_range() - Find a range of Intermediate Physical
  *				     Addresses with compatible permission
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 05321f4165e3..78f36bd5df6c 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -326,6 +326,45 @@ int kvm_pgtable_walk(struct kvm_pgtable *pgt, u64 addr, u64 size,
 	return _kvm_pgtable_walk(&walk_data);
 }
 
+struct leaf_walk_data {
+	kvm_pte_t	pte;
+	u32		level;
+};
+
+static int leaf_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
+		       enum kvm_pgtable_walk_flags flag, void * const arg)
+{
+	struct leaf_walk_data *data = arg;
+
+	data->pte   = *ptep;
+	data->level = level;
+
+	return 0;
+}
+
+int kvm_pgtable_get_leaf(struct kvm_pgtable *pgt, u64 addr,
+			 kvm_pte_t *ptep, u32 *level)
+{
+	struct leaf_walk_data data;
+	struct kvm_pgtable_walker walker = {
+		.cb	= leaf_walker,
+		.flags	= KVM_PGTABLE_WALK_LEAF,
+		.arg	= &data,
+	};
+	int ret;
+
+	ret = kvm_pgtable_walk(pgt, ALIGN_DOWN(addr, PAGE_SIZE),
+			       PAGE_SIZE, &walker);
+	if (!ret) {
+		if (ptep)
+			*ptep  = data.pte;
+		if (level)
+			*level = data.level;
+	}
+
+	return ret;
+}
+
 struct hyp_map_data {
 	u64				phys;
 	kvm_pte_t			attr;
-- 
2.32.0.605.g8dce9f2422-goog