From 7cc1d214a6cd39d7af13f931c8134c24e33dd7f6 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Tue, 23 Apr 2024 16:05:16 +0100 Subject: [PATCH] KVM: arm64: Avoid BBM when changing only s/w bits in Stage-2 PTE Break-before-make (BBM) can be expensive, as transitioning via an invalid mapping (i.e. the "break" step) requires the completion of TLB invalidation and can also cause other agents to fault concurrently on the invalid mapping. Since BBM is not required when changing only the software bits of a PTE, avoid the sequence in this case and just update the PTE directly. Signed-off-by: Will Deacon Signed-off-by: Fuad Tabba Acked-by: Oliver Upton Link: https://lore.kernel.org/r/20240423150538.2103045-9-tabba@google.com Signed-off-by: Marc Zyngier --- arch/arm64/kvm/hyp/pgtable.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c index da54bb3129106..d177a9f7a0977 100644 --- a/arch/arm64/kvm/hyp/pgtable.c +++ b/arch/arm64/kvm/hyp/pgtable.c @@ -972,6 +972,21 @@ static int stage2_map_walker_try_leaf(const struct kvm_pgtable_visit_ctx *ctx, if (!stage2_pte_needs_update(ctx->old, new)) return -EAGAIN; + /* If we're only changing software bits, then store them and go! */ + if (!kvm_pgtable_walk_shared(ctx) && + !((ctx->old ^ new) & ~KVM_PTE_LEAF_ATTR_HI_SW)) { + bool old_is_counted = stage2_pte_is_counted(ctx->old); + + if (old_is_counted != stage2_pte_is_counted(new)) { + if (old_is_counted) + mm_ops->put_page(ctx->ptep); + else + mm_ops->get_page(ctx->ptep); + } + WARN_ON_ONCE(!stage2_try_set_pte(ctx, new)); + return 0; + } + if (!stage2_try_break_pte(ctx, data->mmu)) return -EAGAIN; -- 2.30.2