| Message ID | 20221107215644.1895162-6-oliver.upton@linux.dev (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: arm64: Parallel stage-2 fault handling | expand |
On Mon, Nov 7, 2022 at 1:57 PM Oliver Upton <oliver.upton@linux.dev> 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@linux.dev> > --- > 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 >
On Wed, Nov 09, 2022 at 02:23:33PM -0800, Ben Gardon wrote: > On Mon, Nov 7, 2022 at 1:57 PM Oliver Upton <oliver.upton@linux.dev> 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@linux.dev> > > --- > > 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. No, but this is a pretty obvious problem with all of our table walkers, which led to commit 5994bc9e05c2 ("KVM: arm64: Limit stage2_apply_range() batch size to largest block"). We're lucky in that the largest supported granule across all page table sizes is 1GB (no true 5-level paging yet), so it may not be too horrendous. But yeah, it is on the list of things to fix :) -- Thanks, Oliver
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)); +}
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@linux.dev> --- arch/arm64/include/asm/kvm_pgtable.h | 11 +++++++++++ arch/arm64/kvm/hyp/pgtable.c | 23 +++++++++++++++++++++++ 2 files changed, 34 insertions(+)