On Mon, Nov 7, 2022 at 1:57 PM Oliver Upton <oliver.upton@xxxxxxxxx> wrote:
>
> A subsequent change to KVM will move the tear down of an unlinked
> stage-2 subtree out of the critical path of the break-before-make
> sequence.
>
> Introduce a new helper for tearing down unlinked stage-2 subtrees.
> Leverage the existing stage-2 free walkers to do so, with a deep call
> into __kvm_pgtable_walk() as the subtree is no longer reachable from the
> root.
>
> Signed-off-by: Oliver Upton <oliver.upton@xxxxxxxxx>
> ---
> arch/arm64/include/asm/kvm_pgtable.h | 11 +++++++++++
> arch/arm64/kvm/hyp/pgtable.c | 23 +++++++++++++++++++++++
> 2 files changed, 34 insertions(+)
>
> diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
> index a752793482cb..93b1feeaebab 100644
> --- a/arch/arm64/include/asm/kvm_pgtable.h
> +++ b/arch/arm64/include/asm/kvm_pgtable.h
> @@ -333,6 +333,17 @@ int __kvm_pgtable_stage2_init(struct kvm_pgtable *pgt, struct kvm_s2_mmu *mmu,
> */
> void kvm_pgtable_stage2_destroy(struct kvm_pgtable *pgt);
>
> +/**
> + * kvm_pgtable_stage2_free_removed() - Free a removed stage-2 paging structure.
> + * @mm_ops: Memory management callbacks.
> + * @pgtable: Unlinked stage-2 paging structure to be freed.
> + * @level: Level of the stage-2 paging structure to be freed.
> + *
> + * The page-table is assumed to be unreachable by any hardware walkers prior to
> + * freeing and therefore no TLB invalidation is performed.
> + */
> +void kvm_pgtable_stage2_free_removed(struct kvm_pgtable_mm_ops *mm_ops, void *pgtable, u32 level);
> +
> /**
> * 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 93989b750a26..363a5cce7e1a 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -1203,3 +1203,26 @@ void kvm_pgtable_stage2_destroy(struct kvm_pgtable *pgt)
> pgt->mm_ops->free_pages_exact(pgt->pgd, pgd_sz);
> pgt->pgd = NULL;
> }
> +
> +void kvm_pgtable_stage2_free_removed(struct kvm_pgtable_mm_ops *mm_ops, void *pgtable, u32 level)
> +{
> + kvm_pte_t *ptep = (kvm_pte_t *)pgtable;
> + struct kvm_pgtable_walker walker = {
> + .cb = stage2_free_walker,
> + .flags = KVM_PGTABLE_WALK_LEAF |
> + KVM_PGTABLE_WALK_TABLE_POST,
> + };
> + struct kvm_pgtable_walk_data data = {
> + .walker = &walker,
> +
> + /*
> + * At this point the IPA really doesn't matter, as the page
> + * table being traversed has already been removed from the stage
> + * 2. Set an appropriate range to cover the entire page table.
> + */
> + .addr = 0,
> + .end = kvm_granule_size(level),
> + };
> +
> + WARN_ON(__kvm_pgtable_walk(&data, mm_ops, ptep, level));
> +}
Will this callback be able to yield? In my experience, if processing a
large teardown (i.e. level >=3 / maps 512G region) it's possible to
hit scheduler tick warnings.
> --
> 2.38.1.431.g37b22c650d-goog
>
