Hi, Ricardo
On 2023/1/13 11:49, Ricardo Koller wrote:
> Add a new stage2 function, kvm_pgtable_stage2_split(), for splitting a
> range of huge pages. This will be used for eager-splitting huge pages
> into PAGE_SIZE pages. The goal is to avoid having to split huge pages
> on write-protection faults, and instead use this function to do it
> ahead of time for large ranges (e.g., all guest memory in 1G chunks at
> a time).
>
> No functional change intended. This new function will be used in a
> subsequent commit.
>
> Signed-off-by: Ricardo Koller <ricarkol@xxxxxxxxxx>
> ---
> arch/arm64/include/asm/kvm_pgtable.h | 29 ++++++++++++
> arch/arm64/kvm/hyp/pgtable.c | 67 ++++++++++++++++++++++++++++
> 2 files changed, 96 insertions(+)
>
> diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
> index 8ad78d61af7f..5fbdc1f259fd 100644
> --- a/arch/arm64/include/asm/kvm_pgtable.h
> +++ b/arch/arm64/include/asm/kvm_pgtable.h
> @@ -644,6 +644,35 @@ bool kvm_pgtable_stage2_is_young(struct kvm_pgtable *pgt, u64 addr);
> */
> int kvm_pgtable_stage2_flush(struct kvm_pgtable *pgt, u64 addr, u64 size);
>
> +/**
> + * kvm_pgtable_stage2_split() - Split a range of huge pages into leaf PTEs pointing
> + * to PAGE_SIZE guest pages.
> + * @pgt: Page-table structure initialised by kvm_pgtable_stage2_init*().
> + * @addr: Intermediate physical address from which to split.
> + * @size: Size of the range.
> + * @mc: Cache of pre-allocated and zeroed memory from which to allocate
> + * page-table pages.
> + *
> + * @addr and the end (@addr + @size) are effectively aligned down and up to
> + * the top level huge-page block size. This is an exampe using 1GB
> + * huge-pages and 4KB granules.
> + *
> + * [---input range---]
> + * : :
> + * [--1G block pte--][--1G block pte--][--1G block pte--][--1G block pte--]
> + * : :
> + * [--2MB--][--2MB--][--2MB--][--2MB--]
> + * : :
> + * [ ][ ][:][ ][ ][ ][ ][ ][:][ ][ ][ ]
> + * : :
> + *
> + * Return: 0 on success, negative error code on failure. Note that
> + * kvm_pgtable_stage2_split() is best effort: it tries to break as many
> + * blocks in the input range as allowed by the size of the memcache. It
> + * will fail it wasn't able to break any block.
> + */
> +int kvm_pgtable_stage2_split(struct kvm_pgtable *pgt, u64 addr, u64 size, void *mc);
> +
> /**
> * 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 0dee13007776..db9d1a28769b 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -1229,6 +1229,73 @@ int kvm_pgtable_stage2_create_removed(struct kvm_pgtable *pgt,
> return 0;
> }
>
> +struct stage2_split_data {
> + struct kvm_s2_mmu *mmu;
> + void *memcache;
> +};
> +
> +static int stage2_split_walker(const struct kvm_pgtable_visit_ctx *ctx,
> + enum kvm_pgtable_walk_flags visit)
> +{
> + struct stage2_split_data *data = ctx->arg;
> + struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
> + kvm_pte_t pte = ctx->old, new, *childp;
> + enum kvm_pgtable_prot prot;
> + void *mc = data->memcache;
> + u32 level = ctx->level;
> + u64 phys;
> + int ret;
> +
> + /* Nothing to split at the last level */
> + if (level == KVM_PGTABLE_MAX_LEVELS - 1)
> + return 0;
> +
> + /* We only split valid block mappings */
> + if (!kvm_pte_valid(pte) || kvm_pte_table(pte, ctx->level))
> + return 0;
> +
IIUC, It should be !kvm_pte_table(pte, ctx->level)?
also, the kvm_pte_table includes the level check and kvm_pte_valid, so, it just be like:
- /* Nothing to split at the last level */
- if (level == KVM_PGTABLE_MAX_LEVELS - 1)
- return 0;
-
- /* We only split valid block mappings */
+ if (!kvm_pte_table(pte, ctx->level))
+ return 0;
> + phys = kvm_pte_to_phys(pte);
> + prot = kvm_pgtable_stage2_pte_prot(pte);
> +
> + ret = kvm_pgtable_stage2_create_removed(data->mmu->pgt, &new, phys,
> + level, prot, mc);
> + if (ret)
> + return ret;
> +
> + if (!stage2_try_break_pte(ctx, data->mmu)) {
> + childp = kvm_pte_follow(new, mm_ops);
> + kvm_pgtable_stage2_free_removed(mm_ops, childp, level);
> + mm_ops->put_page(childp);
> + return -EAGAIN;
> + }
> +
> + /*
> + * Note, the contents of the page table are guaranteed to be
> + * made visible before the new PTE is assigned because
> + * stage2_make_pte() writes the PTE using smp_store_release().
> + */
> + stage2_make_pte(ctx, new);
> + dsb(ishst);
> + return 0;
> +}
> +
> +int kvm_pgtable_stage2_split(struct kvm_pgtable *pgt,
> + u64 addr, u64 size, void *mc)
> +{
> + struct stage2_split_data split_data = {
> + .mmu = pgt->mmu,
> + .memcache = mc,
> + };
> +
> + struct kvm_pgtable_walker walker = {
> + .cb = stage2_split_walker,
> + .flags = KVM_PGTABLE_WALK_LEAF,
> + .arg = &split_data,
> + };
> +
> + return kvm_pgtable_walk(pgt, addr, size, &walker);
> +}
> +
> int __kvm_pgtable_stage2_init(struct kvm_pgtable *pgt, struct kvm_s2_mmu *mmu,
> struct kvm_pgtable_mm_ops *mm_ops,
> enum kvm_pgtable_stage2_flags flags,
>
--
Regards.
Chuan
