On Mon, Nov 7, 2022 at 1:57 PM Oliver Upton <oliver.upton@xxxxxxxxx> wrote:
>
> 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@xxxxxxxxx>
> ---
> arch/arm64/include/asm/kvm_pgtable.h | 9 ++++++++-
> arch/arm64/kvm/hyp/pgtable.c | 27 ++++++++++++++-------------
> arch/arm64/kvm/mmu.c | 2 +-
> 3 files changed, 23 insertions(+), 15 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
> index 93b1feeaebab..cbd2851eefc1 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)
Since shared is not used and never true as of this commit, it would
probably be worth explaining what it's for in the change description.
> +{
> + return pteref;
> +}
> +
> #define KVM_PTE_VALID BIT(0)
>
> #define KVM_PTE_ADDR_MASK GENMASK(47, PAGE_SHIFT)
> @@ -175,7 +182,7 @@ 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 363a5cce7e1a..7511494537e5 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;
>
> @@ -544,7 +545,7 @@ void kvm_pgtable_hyp_destroy(struct kvm_pgtable *pgt)
> };
>
> WARN_ON(kvm_pgtable_walk(pgt, 0, BIT(pgt->ia_bits), &walker));
> - pgt->mm_ops->put_page(pgt->pgd);
> + pgt->mm_ops->put_page(kvm_dereference_pteref(pgt->pgd, false));
> pgt->pgd = NULL;
> }
>
> @@ -1157,7 +1158,7 @@ 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;
>
> @@ -1200,7 +1201,7 @@ void kvm_pgtable_stage2_destroy(struct kvm_pgtable *pgt)
>
> WARN_ON(kvm_pgtable_walk(pgt, 0, BIT(pgt->ia_bits), &walker));
> pgd_sz = kvm_pgd_pages(pgt->ia_bits, pgt->start_level) * PAGE_SIZE;
> - pgt->mm_ops->free_pages_exact(pgt->pgd, pgd_sz);
> + pgt->mm_ops->free_pages_exact(kvm_dereference_pteref(pgt->pgd, false), pgd_sz);
> pgt->pgd = NULL;
> }
>
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 60ee3d9f01f8..5e197ae190ef 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -640,7 +640,7 @@ static struct kvm_pgtable_mm_ops kvm_user_mm_ops = {
> static int get_user_mapping_size(struct kvm *kvm, u64 addr)
> {
> struct kvm_pgtable pgt = {
> - .pgd = (kvm_pte_t *)kvm->mm->pgd,
> + .pgd = (kvm_pteref_t)kvm->mm->pgd,
> .ia_bits = VA_BITS,
> .start_level = (KVM_PGTABLE_MAX_LEVELS -
> CONFIG_PGTABLE_LEVELS),
> --
> 2.38.1.431.g37b22c650d-goog
>
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