From 66751b515c340db6e2ce66e19421eeb11d2d7b91 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Wed, 10 Nov 2021 12:31:25 +0000 Subject: [PATCH] ANDROID: 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: Will Deacon Bug: 233587962 Change-Id: I91ec043a75154fa2ca732f5269c6ae1bceea4a93 --- arch/arm64/kvm/hyp/pgtable.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c index 1597b388d12e..b5e183f6f5a9 100644 --- a/arch/arm64/kvm/hyp/pgtable.c +++ b/arch/arm64/kvm/hyp/pgtable.c @@ -732,6 +732,13 @@ static int stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level, if (!stage2_pte_needs_update(old, new)) return -EAGAIN; + /* + * If we're only changing software bits, then we don't need to + * do anything else/ + */ + if (!((old ^ new) & ~KVM_PTE_LEAF_ATTR_HI_SW)) + goto out_set_pte; + stage2_put_pte(ptep, data->mmu, addr, level, mm_ops); } @@ -742,9 +749,11 @@ static int stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level, if (mm_ops->icache_inval_pou && stage2_pte_executable(new)) mm_ops->icache_inval_pou(kvm_pte_follow(new, mm_ops), granule); - smp_store_release(ptep, new); if (stage2_pte_is_counted(new)) mm_ops->get_page(ptep); + +out_set_pte: + smp_store_release(ptep, new); if (kvm_phys_is_valid(phys)) data->phys += granule; return 0;