On Wed, Feb 8, 2023 at 9:58 PM Gavin Shan <gshan@xxxxxxxxxx> wrote:
>
> Hi Ricardo,
>
> On 2/7/23 3:58 AM, 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 | 30 ++++++++
> > arch/arm64/kvm/hyp/pgtable.c | 105 +++++++++++++++++++++++++++
> > 2 files changed, 135 insertions(+)
> >
> > diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
> > index e94c92988745..871c4eeb0184 100644
> > --- a/arch/arm64/include/asm/kvm_pgtable.h
> > +++ b/arch/arm64/include/asm/kvm_pgtable.h
> > @@ -658,6 +658,36 @@ 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.
> > + * @mc_capacity: Number of pages in @mc.
> > + *
> > + * @addr and the end (@addr + @size) are effectively aligned down and up to
> > + * the top level huge-page block size. This is an example 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 @mc_capacity.
> > + */
> > +int kvm_pgtable_stage2_split(struct kvm_pgtable *pgt, u64 addr, u64 size,
> > + void *mc, u64 mc_capacity);
> > +
> > /**
> > * 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 fed314f2b320..ae80845c8db7 100644
> > --- a/arch/arm64/kvm/hyp/pgtable.c
> > +++ b/arch/arm64/kvm/hyp/pgtable.c
> > @@ -1229,6 +1229,111 @@ int kvm_pgtable_stage2_create_unlinked(struct kvm_pgtable *pgt,
> > return 0;
> > }
> >
> > +struct stage2_split_data {
> > + struct kvm_s2_mmu *mmu;
> > + void *memcache;
> > + u64 mc_capacity;
> > +};
> > +
> > +/*
> > + * Get the number of page-tables needed to replace a bock with a fully
> > + * populated tree, up to the PTE level, at particular level.
> > + */
> > +static inline u32 stage2_block_get_nr_page_tables(u32 level)
> > +{
> > + switch (level) {
> > + /* There are no blocks at level 0 */
> > + case 1: return 1 + PTRS_PER_PTE;
> > + case 2: return 1;
> > + case 3: return 0;
> > + default:
> > + WARN_ON_ONCE(1);
> > + return ~0;
> > + }
> > +}
> > +
> > +static int stage2_split_walker(const struct kvm_pgtable_visit_ctx *ctx,
> > + enum kvm_pgtable_walk_flags visit)
> > +{
> > + struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
> > + struct stage2_split_data *data = ctx->arg;
> > + kvm_pte_t pte = ctx->old, new, *childp;
> > + enum kvm_pgtable_prot prot;
> > + void *mc = data->memcache;
> > + u32 level = ctx->level;
> > + u64 phys, nr_pages;
> > + bool force_pte;
> > + int ret;
> > +
> > + /* No huge-pages exist 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;
> > +
>
> Since stage2_split_walker() has been specified as a leaf walker by KVM_PGTABLE_WALK_LEAF,
> I don't understand how kvm_pte_table() can return true.
Good point. Will remove it. This check made sense for a previous
version (the RFC),
but not anymore.
>
> > + nr_pages = stage2_block_get_nr_page_tables(level);
> > + if (data->mc_capacity >= nr_pages) {
> > + /* Build a tree mapped down to the PTE granularity. */
> > + force_pte = true;
> > + } else {
> > + /*
> > + * Don't force PTEs. This requires a single page of PMDs at the
> > + * PUD level, or a single page of PTEs at the PMD level. If we
> > + * are at the PUD level, the PTEs will be created recursively.
> > + */
> > + force_pte = false;
> > + nr_pages = 1;
> > + }
> > +
> > + if (data->mc_capacity < nr_pages)
> > + return -ENOMEM;
> > +
> > + phys = kvm_pte_to_phys(pte);
> > + prot = kvm_pgtable_stage2_pte_prot(pte);
> > +
> > + ret = kvm_pgtable_stage2_create_unlinked(data->mmu->pgt, &new, phys,
> > + level, prot, mc, force_pte);
> > + if (ret)
> > + return ret;
> > +
> > + if (!stage2_try_break_pte(ctx, data->mmu)) {
> > + childp = kvm_pte_follow(new, mm_ops);
> > + kvm_pgtable_stage2_free_unlinked(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);
> > + data->mc_capacity -= nr_pages;
> > + return 0;
> > +}
> > +
>
> I think it's possible 'data->mc_capability' to be replaced by 'mc->nobjs'
> because they're same thing. With this, we needn't to maintain a duplicate
> 'data->mc_capability' since 'data->mc' has been existing.
Ah, nice, yes. That would be simpler.
Thanks!
Ricardo
>
> > +int kvm_pgtable_stage2_split(struct kvm_pgtable *pgt, u64 addr, u64 size,
> > + void *mc, u64 mc_capacity)
> > +{
> > + struct stage2_split_data split_data = {
> > + .mmu = pgt->mmu,
> > + .memcache = mc,
> > + .mc_capacity = mc_capacity,
> > + };
> > +
> > + 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,
> >
>
> Thanks,
> Gavin
>
