On 4/9/23 2:29 PM, 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).
Signed-off-by: Ricardo Koller <ricarkol@xxxxxxxxxx>
Reviewed-by: Shaoqin Huang <shahuang@xxxxxxxxxx>
---
arch/arm64/include/asm/kvm_pgtable.h | 19 +++++
arch/arm64/kvm/hyp/pgtable.c | 103 +++++++++++++++++++++++++++
2 files changed, 122 insertions(+)
With the following nits addressed:
Reviewed-by: Gavin Shan <gshan@xxxxxxxxxx>
diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index c8e0e7d9303b2..32e5d42bf020f 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -653,6 +653,25 @@ 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
^^^^^^^^
Alignment.
+ * page-table pages.
+ *
+ * The function tries to split any level 1 or 2 entry that overlaps
+ * with the input range (given by @addr and @size).
+ *
+ * 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,
+ struct kvm_mmu_memory_cache *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 477d2be67d401..48c5a95c6e8cd 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -1272,6 +1272,109 @@ kvm_pte_t *kvm_pgtable_stage2_create_unlinked(struct kvm_pgtable *pgt,
return pgtable;
}
+/*
+ * Get the number of page-tables needed to replace a block with a
+ * fully populated tree up to the PTE entries. Note that @level is
+ * interpreted as in "level @level entry".
+ */
+static int stage2_block_get_nr_page_tables(u32 level)
+{
+ switch (level) {
+ case 1:
+ return PTRS_PER_PTE + 1;
+ case 2:
+ return 1;
+ case 3:
+ return 0;
+ default:
+ WARN_ON_ONCE(level < KVM_PGTABLE_MIN_BLOCK_LEVEL ||
+ level >= KVM_PGTABLE_MAX_LEVELS);
+ return -EINVAL;
+ };
+}
+
When the starting level is 3, it's not a block mapping if I'm correct. Besides,
the caller (stage2_split_walker()) bails when the starting level is 3. In this
case, the changes may be integrated to stage2_split_walker(), which is the only
caller. Otherwise, 'inline' is worthy to have.
nr_pages = kvm_granule_shift(level) == PUD_SHIFT && kvm_granule_shift(level) != PMD_SHIFT) ?
(PTRS_PER_PTE + 1) : 1;
+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 kvm_mmu_memory_cache *mc = ctx->arg;
+ struct kvm_s2_mmu *mmu;
+ kvm_pte_t pte = ctx->old, new, *childp;
+ enum kvm_pgtable_prot prot;
+ u32 level = ctx->level;
+ bool force_pte;
+ int nr_pages;
+ u64 phys;
+
+ /* 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))
+ return 0;
+
+ nr_pages = stage2_block_get_nr_page_tables(level);
+ if (nr_pages < 0)
+ return nr_pages;
+
+ if (mc->nobjs >= nr_pages) {
+ /* Build a tree mapped down to the PTE granularity. */
+ force_pte = true;
+ } else {
+ /*
+ * Don't force PTEs, so create_unlinked() below does
+ * not populate the tree up to the PTE level. The
+ * consequence is that the call will require a single
+ * page of level 2 entries at level 1, or a single
+ * page of PTEs at level 2. If we are at level 1, the
+ * PTEs will be created recursively.
+ */
+ force_pte = false;
+ nr_pages = 1;
+ }
+
+ if (mc->nobjs < nr_pages)
+ return -ENOMEM;
+
+ mmu = container_of(mc, struct kvm_s2_mmu, split_page_cache);
+ phys = kvm_pte_to_phys(pte);
+ prot = kvm_pgtable_stage2_pte_prot(pte);
+
+ childp = kvm_pgtable_stage2_create_unlinked(mmu->pgt, phys,
+ level, prot, mc, force_pte);
+ if (IS_ERR(childp))
+ return PTR_ERR(childp);
+
+ if (!stage2_try_break_pte(ctx, mmu)) {
+ 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().
+ */
+ new = kvm_init_table_pte(childp, mm_ops);
+ stage2_make_pte(ctx, new);
+ dsb(ishst);
+ return 0;
+}
+
+int kvm_pgtable_stage2_split(struct kvm_pgtable *pgt, u64 addr, u64 size,
+ struct kvm_mmu_memory_cache *mc)
+{
+ struct kvm_pgtable_walker walker = {
+ .cb = stage2_split_walker,
+ .flags = KVM_PGTABLE_WALK_LEAF,
+ .arg = mc,
+ };
+
+ 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
