On Thu, Jan 12, 2023 at 7:50 PM Ricardo Koller <ricarkol@xxxxxxxxxx> wrote:
>
> Add a stage2 helper, kvm_pgtable_stage2_create_removed(), for creating
> removed tables (the opposite of kvm_pgtable_stage2_free_removed()).
> Creating a removed table is useful for splitting block PTEs into
> subtrees of 4K PTEs. For example, a 1G block PTE can be split into 4K
> PTEs by first creating a fully populated tree, and then use it to
> replace the 1G PTE in a single step. This will be used in a
> subsequent commit for eager huge-page splitting (a dirty-logging
> optimization).
>
> 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 | 25 +++++++++++++++
> arch/arm64/kvm/hyp/pgtable.c | 47 ++++++++++++++++++++++++++++
> 2 files changed, 72 insertions(+)
>
> diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
> index 84a271647007..8ad78d61af7f 100644
> --- a/arch/arm64/include/asm/kvm_pgtable.h
> +++ b/arch/arm64/include/asm/kvm_pgtable.h
> @@ -450,6 +450,31 @@ void kvm_pgtable_stage2_destroy(struct kvm_pgtable *pgt);
> */
> void kvm_pgtable_stage2_free_removed(struct kvm_pgtable_mm_ops *mm_ops, void *pgtable, u32 level);
>
> +/**
> + * kvm_pgtable_stage2_free_removed() - Create a removed stage-2 paging structure.
> + * @pgt: Page-table structure initialised by kvm_pgtable_stage2_init*().
> + * @new: Unlinked stage-2 paging structure to be created.
Oh, I see so the "removed" page table is actually a new page table
that has never been part of the paging structure. In that case I would
find it much more intuitive to call it "unlinked" or similar.
> + * @phys: Physical address of the memory to map.
> + * @level: Level of the stage-2 paging structure to be created.
> + * @prot: Permissions and attributes for the mapping.
> + * @mc: Cache of pre-allocated and zeroed memory from which to allocate
> + * page-table pages.
> + *
> + * Create a removed page-table tree of PAGE_SIZE leaf PTEs under *new.
> + * This new page-table tree is not reachable (i.e., it is removed) from the
> + * root pgd and it's therefore unreachableby the hardware page-table
> + * walker. No TLB invalidation or CMOs are performed.
> + *
> + * If device attributes are not explicitly requested in @prot, then the
> + * mapping will be normal, cacheable.
> + *
> + * Return: 0 only if a fully populated tree was created, negative error
> + * code on failure. No partially-populated table can be returned.
> + */
> +int kvm_pgtable_stage2_create_removed(struct kvm_pgtable *pgt,
> + kvm_pte_t *new, u64 phys, u32 level,
> + enum kvm_pgtable_prot prot, void *mc);
> +
> /**
> * kvm_pgtable_stage2_map() - Install a mapping in a guest stage-2 page-table.
> * @pgt: Page-table structure initialised by kvm_pgtable_stage2_init*().
> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index 87fd40d09056..0dee13007776 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -1181,6 +1181,53 @@ int kvm_pgtable_stage2_flush(struct kvm_pgtable *pgt, u64 addr, u64 size)
> return kvm_pgtable_walk(pgt, addr, size, &walker);
> }
>
> +/*
> + * map_data->force_pte is true in order to force creating PAGE_SIZE PTEs.
> + * data->addr is 0 because the IPA is irrelevant for a removed table.
> + */
> +int kvm_pgtable_stage2_create_removed(struct kvm_pgtable *pgt,
> + kvm_pte_t *new, u64 phys, u32 level,
> + enum kvm_pgtable_prot prot, void *mc)
> +{
> + struct stage2_map_data map_data = {
> + .phys = phys,
> + .mmu = pgt->mmu,
> + .memcache = mc,
> + .force_pte = true,
> + };
> + struct kvm_pgtable_walker walker = {
> + .cb = stage2_map_walker,
> + .flags = KVM_PGTABLE_WALK_LEAF |
> + KVM_PGTABLE_WALK_REMOVED,
> + .arg = &map_data,
> + };
> + struct kvm_pgtable_walk_data data = {
> + .walker = &walker,
> + .addr = 0,
> + .end = kvm_granule_size(level),
> + };
> + struct kvm_pgtable_mm_ops *mm_ops = pgt->mm_ops;
> + kvm_pte_t *pgtable;
> + int ret;
> +
> + ret = stage2_set_prot_attr(pgt, prot, &map_data.attr);
> + if (ret)
> + return ret;
> +
> + pgtable = mm_ops->zalloc_page(mc);
> + if (!pgtable)
> + return -ENOMEM;
> +
> + ret = __kvm_pgtable_walk(&data, mm_ops, pgtable, level + 1);
> + if (ret) {
> + kvm_pgtable_stage2_free_removed(mm_ops, pgtable, level);
> + mm_ops->put_page(pgtable);
> + return ret;
> + }
> +
> + *new = kvm_init_table_pte(pgtable, mm_ops);
> + return 0;
> +}
>
> int __kvm_pgtable_stage2_init(struct kvm_pgtable *pgt, struct kvm_s2_mmu *mmu,
> struct kvm_pgtable_mm_ops *mm_ops,
> --
> 2.39.0.314.g84b9a713c41-goog
>
