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KVM: arm64: Only drop references on empty tables in stage2_free_walker

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A subsequent change to the way KVM frees stage-2s will invoke the free
walker on sub-ranges of the VM's IPA space, meaning there's potential
for only partially visiting a table's PTEs.

Split the leaf and table visitors and only drop references on a table
when the page count reaches 1, implying there are no valid PTEs that
need to be visited. Invalidate the table PTE to avoid traversing the
stale reference.

Link: https://msgid.link/20251113052452.975081-2-rananta@google.com
Signed-off-by: Oliver Upton <oupton@kernel.org>
This commit is contained in:
Oliver Upton
2025-11-19 14:11:50 -08:00
parent 85f329df29
commit 156f70afcf
1 changed files with 34 additions and 8 deletions
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42
arch/arm64/kvm/hyp/pgtable.c
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@@ -1535,20 +1535,46 @@ size_t kvm_pgtable_stage2_pgd_size(u64 vtcr)
return kvm_pgd_pages(ia_bits, start_level) * PAGE_SIZE; return kvm_pgd_pages(ia_bits, start_level) * PAGE_SIZE;
} }
static int stage2_free_walker(const struct kvm_pgtable_visit_ctx *ctx, static int stage2_free_leaf(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_pgtable_mm_ops *mm_ops = ctx->mm_ops;
mm_ops->put_page(ctx->ptep);
return 0;
}
static int stage2_free_table_post(const struct kvm_pgtable_visit_ctx *ctx)
{
struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
kvm_pte_t *childp = kvm_pte_follow(ctx->old, mm_ops);
if (mm_ops->page_count(childp) != 1)
return 0;
/*
* Drop references and clear the now stale PTE to avoid rewalking the
* freed page table.
*/
mm_ops->put_page(ctx->ptep);
mm_ops->put_page(childp);
kvm_clear_pte(ctx->ptep);
return 0;
}
static int stage2_free_walker(const struct kvm_pgtable_visit_ctx *ctx,
enum kvm_pgtable_walk_flags visit)
{
if (!stage2_pte_is_counted(ctx->old)) if (!stage2_pte_is_counted(ctx->old))
return 0; return 0;
mm_ops->put_page(ctx->ptep); switch (visit) {
case KVM_PGTABLE_WALK_LEAF:
if (kvm_pte_table(ctx->old, ctx->level)) return stage2_free_leaf(ctx);
mm_ops->put_page(kvm_pte_follow(ctx->old, mm_ops)); case KVM_PGTABLE_WALK_TABLE_POST:
return stage2_free_table_post(ctx);
return 0; default:
return -EINVAL;
}
} }
void kvm_pgtable_stage2_destroy(struct kvm_pgtable *pgt) void kvm_pgtable_stage2_destroy(struct kvm_pgtable *pgt)