[PATCH v3 07/15] KVM: arm64: Use an opaque type for pteps

Oliver Upton
2022-10-27T22:19:36Z

Use an opaque type for pteps and require visitors explicitly dereference
the pointer before using. Protecting page table memory with RCU requires
that KVM dereferences RCU-annotated pointers before using. However, RCU
is not available for use in the nVHE hypervisor and the opaque type can
be conditionally annotated with RCU for the stage-2 MMU.

Call the type a 'pteref' to avoid a naming collision with raw pteps. No
functional change intended.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
arch/arm64/include/asm/kvm_pgtable.h | 9 ++++++++-
arch/arm64/kvm/hyp/pgtable.c | 23 ++++++++++++-----------
2 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index 7a8af3b686e8..e70cf57b719e 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -37,6 +37,13 @@ static inline u64 kvm_get_parange(u64 mmfr0)

typedef u64 kvm_pte_t;

+typedef kvm_pte_t *kvm_pteref_t;
+
+static inline kvm_pte_t *kvm_dereference_pteref(kvm_pteref_t pteref, bool shared)
+{
+ return pteref;
+}
+
#define KVM_PTE_VALID BIT(0)

#define KVM_PTE_ADDR_MASK GENMASK(47, PAGE_SHIFT)
@@ -178,7 +185,7 @@ typedef bool (*kvm_pgtable_force_pte_cb_t)(u64 addr, u64 end,
struct kvm_pgtable {
u32 ia_bits;
u32 start_level;
- kvm_pte_t *pgd;
+ kvm_pteref_t pgd;
struct kvm_pgtable_mm_ops *mm_ops;

/* Stage-2 only */
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 167777b42890..c4d103889a62 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -175,13 +175,14 @@ static int kvm_pgtable_visitor_cb(struct kvm_pgtable_walk_data *data,
}

static int __kvm_pgtable_walk(struct kvm_pgtable_walk_data *data,
- struct kvm_pgtable_mm_ops *mm_ops, kvm_pte_t *pgtable, u32 level);
+ struct kvm_pgtable_mm_ops *mm_ops, kvm_pteref_t pgtable, u32 level);

static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data,
struct kvm_pgtable_mm_ops *mm_ops,
- kvm_pte_t *ptep, u32 level)
+ kvm_pteref_t pteref, u32 level)
{
enum kvm_pgtable_walk_flags flags = data->walker->flags;
+ kvm_pte_t *ptep = kvm_dereference_pteref(pteref, false);
struct kvm_pgtable_visit_ctx ctx = {
.ptep = ptep,
.old = READ_ONCE(*ptep),
@@ -193,7 +194,7 @@ static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data,
.flags = flags,
};
int ret = 0;
- kvm_pte_t *childp;
+ kvm_pteref_t childp;
bool table = kvm_pte_table(ctx.old, level);

if (table && (ctx.flags & KVM_PGTABLE_WALK_TABLE_PRE))
@@ -214,7 +215,7 @@ static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data,
goto out;
}

- childp = kvm_pte_follow(ctx.old, mm_ops);
+ childp = (kvm_pteref_t)kvm_pte_follow(ctx.old, mm_ops);
ret = __kvm_pgtable_walk(data, mm_ops, childp, level + 1);
if (ret)
goto out;
@@ -227,7 +228,7 @@ static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data,
}

static int __kvm_pgtable_walk(struct kvm_pgtable_walk_data *data,
- struct kvm_pgtable_mm_ops *mm_ops, kvm_pte_t *pgtable, u32 level)
+ struct kvm_pgtable_mm_ops *mm_ops, kvm_pteref_t pgtable, u32 level)
{
u32 idx;
int ret = 0;
@@ -236,12 +237,12 @@ static int __kvm_pgtable_walk(struct kvm_pgtable_walk_data *data,
return -EINVAL;

for (idx = kvm_pgtable_idx(data, level); idx < PTRS_PER_PTE; ++idx) {
- kvm_pte_t *ptep = &pgtable[idx];
+ kvm_pteref_t pteref = &pgtable[idx];

if (data->addr >= data->end)
break;

- ret = __kvm_pgtable_visit(data, mm_ops, ptep, level);
+ ret = __kvm_pgtable_visit(data, mm_ops, pteref, level);
if (ret)
break;
}
@@ -262,9 +263,9 @@ static int _kvm_pgtable_walk(struct kvm_pgtable *pgt, struct kvm_pgtable_walk_da
return -EINVAL;

for (idx = kvm_pgd_page_idx(pgt, data->addr); data->addr < data->end; ++idx) {
- kvm_pte_t *ptep = &pgt->pgd[idx * PTRS_PER_PTE];
+ kvm_pteref_t pteref = &pgt->pgd[idx * PTRS_PER_PTE];

- ret = __kvm_pgtable_walk(data, pgt->mm_ops, ptep, pgt->start_level);
+ ret = __kvm_pgtable_walk(data, pgt->mm_ops, pteref, pgt->start_level);
if (ret)
break;
}
@@ -507,7 +508,7 @@ int kvm_pgtable_hyp_init(struct kvm_pgtable *pgt, u32 va_bits,
{
u64 levels = ARM64_HW_PGTABLE_LEVELS(va_bits);

- pgt->pgd = (kvm_pte_t *)mm_ops->zalloc_page(NULL);
+ pgt->pgd = (kvm_pteref_t)mm_ops->zalloc_page(NULL);
if (!pgt->pgd)
return -ENOMEM;

@@ -1116,7 +1117,7 @@ int __kvm_pgtable_stage2_init(struct kvm_pgtable *pgt, struct kvm_s2_mmu *mmu,
u32 start_level = VTCR_EL2_TGRAN_SL0_BASE - sl0;

pgd_sz = kvm_pgd_pages(ia_bits, start_level) * PAGE_SIZE;
- pgt->pgd = mm_ops->zalloc_pages_exact(pgd_sz);
+ pgt->pgd = (kvm_pteref_t)mm_ops->zalloc_pages_exact(pgd_sz);
if (!pgt->pgd)
return -ENOMEM;

--
2.38.1.273.g43a17bfeac-goog