From c20fef387cd27d1df6b1e156f615e09259120277 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 Bug: 209580772 Change-Id: Ib4858b2491b221490b74cb5100474acaad711483 Signed-off-by: Will Deacon --- 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 2cb3867eb7c2..afbebef34044 100644 --- a/arch/arm64/kvm/hyp/pgtable.c +++ b/arch/arm64/kvm/hyp/pgtable.c @@ -744,6 +744,13 @@ 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); } @@ -755,9 +762,11 @@ 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;