[PATCH v3 10/21] KVM: arm64: Add support for stage-2 page-aging in generic page-table

Will Deacon
2020-08-25T09:44:25Z

Add stage-2 mkyoung(), mkold() and is_young() operations to the generic
page-table code.

Cc: Marc Zyngier <maz@kernel.org>
Cc: Quentin Perret <qperret@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
arch/arm64/include/asm/kvm_pgtable.h | 38 ++++++++++++
arch/arm64/kvm/hyp/pgtable.c | 86 ++++++++++++++++++++++++++++
2 files changed, 124 insertions(+)

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index 8ab0d5f43817..ae56534f87a0 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -173,6 +173,44 @@ int kvm_pgtable_stage2_map(struct kvm_pgtable *pgt, u64 addr, u64 size,
*/
int kvm_pgtable_stage2_unmap(struct kvm_pgtable *pgt, u64 addr, u64 size);

+/**
+ * kvm_pgtable_stage2_mkyoung() - Set the access flag in a page-table entry.
+ * @pgt: Page-table structure initialised by kvm_pgtable_stage2_init().
+ * @addr: Intermediate physical address to identify the page-table entry.
+ *
+ * If there is a valid, leaf page-table entry used to translate @addr, then
+ * set the access flag in that entry.
+ *
+ * Return: The old page-table entry prior to setting the flag, 0 on failure.
+ */
+kvm_pte_t kvm_pgtable_stage2_mkyoung(struct kvm_pgtable *pgt, u64 addr);
+
+/**
+ * kvm_pgtable_stage2_mkold() - Clear the access flag in a page-table entry.
+ * @pgt: Page-table structure initialised by kvm_pgtable_stage2_init().
+ * @addr: Intermediate physical address to identify the page-table entry.
+ *
+ * If there is a valid, leaf page-table entry used to translate @addr, then
+ * clear the access flag in that entry.
+ *
+ * Note that it is the caller's responsibility to invalidate the TLB after
+ * calling this function to ensure that the updated permissions are visible
+ * to the CPUs.
+ *
+ * Return: The old page-table entry prior to clearing the flag, 0 on failure.
+ */
+kvm_pte_t kvm_pgtable_stage2_mkold(struct kvm_pgtable *pgt, u64 addr);
+
+/**
+ * kvm_pgtable_stage2_is_young() - Test whether a page-table entry has the
+ * access flag set.
+ * @pgt: Page-table structure initialised by kvm_pgtable_stage2_init().
+ * @addr: Intermediate physical address to identify the page-table entry.
+ *
+ * Return: True if the page-table entry has the access flag set, false otherwise.
+ */
+bool kvm_pgtable_stage2_is_young(struct kvm_pgtable *pgt, u64 addr);
+
/**
* kvm_pgtable_walk() - Walk a page-table.
* @pgt: Page-table structure initialised by kvm_pgtable_*_init().
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 6f65d3841ec9..30713eb773e0 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -670,6 +670,92 @@ int kvm_pgtable_stage2_unmap(struct kvm_pgtable *pgt, u64 addr, u64 size)
return kvm_pgtable_walk(pgt, addr, size, &walker);
}

+struct stage2_attr_data {
+ kvm_pte_t attr_set;
+ kvm_pte_t attr_clr;
+ kvm_pte_t pte;
+};
+
+static int stage2_attr_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
+ enum kvm_pgtable_walk_flags flag,
+ void * const arg)
+{
+ kvm_pte_t pte = *ptep;
+ struct stage2_attr_data *data = arg;
+
+ if (!kvm_pte_valid(pte))
+ return 0;
+
+ data->pte = pte;
+ pte &= ~data->attr_clr;
+ pte |= data->attr_set;
+
+ /*
+ * We may race with the CPU trying to set the access flag here,
+ * but worst-case the access flag update gets lost and will be
+ * set on the next access instead.
+ */
+ if (data->pte != pte)
+ WRITE_ONCE(*ptep, pte);
+
+ return 0;
+}
+
+static int stage2_update_leaf_attrs(struct kvm_pgtable *pgt, u64 addr,
+ u64 size, kvm_pte_t attr_set,
+ kvm_pte_t attr_clr, kvm_pte_t *orig_pte)
+{
+ int ret;
+ kvm_pte_t attr_mask = KVM_PTE_LEAF_ATTR_LO | KVM_PTE_LEAF_ATTR_HI;
+ struct stage2_attr_data data = {
+ .attr_set = attr_set & attr_mask,
+ .attr_clr = attr_clr & attr_mask,
+ };
+ struct kvm_pgtable_walker walker = {
+ .cb = stage2_attr_walker,
+ .arg = &data,
+ .flags = KVM_PGTABLE_WALK_LEAF,
+ };
+
+ ret = kvm_pgtable_walk(pgt, addr, size, &walker);
+ if (ret)
+ return ret;
+
+ if (orig_pte)
+ *orig_pte = data.pte;
+ return 0;
+}
+
+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);
+ dsb(ishst);
+ return pte;
+}
+
+kvm_pte_t kvm_pgtable_stage2_mkold(struct kvm_pgtable *pgt, u64 addr)
+{
+ kvm_pte_t pte = 0;
+ stage2_update_leaf_attrs(pgt, addr, 1, 0, KVM_PTE_LEAF_ATTR_LO_S2_AF,
+ &pte);
+ /*
+ * "But where's the TLBI?!", you scream.
+ * "Over in the core code", I sigh.
+ *
+ * See the '->clear_flush_young()' callback on the KVM mmu notifier.
+ */
+ return pte;
+}
+
+bool kvm_pgtable_stage2_is_young(struct kvm_pgtable *pgt, u64 addr)
+{
+ kvm_pte_t pte = 0;
+ stage2_update_leaf_attrs(pgt, addr, 1, 0, 0, &pte);
+ return pte & KVM_PTE_LEAF_ATTR_LO_S2_AF;
+}
+
int kvm_pgtable_stage2_init(struct kvm_pgtable *pgt, struct kvm *kvm)
{
size_t pgd_sz;
--
2.28.0.297.g1956fa8f8d-goog