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ANDROID: KVM: arm64: Avoid BBM when changing only s/w bits in Stage-2 PTE

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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 <will@kernel.org>
Bug: 209580772
Change-Id: Ib4858b2491b221490b74cb5100474acaad711483
Signed-off-by: Will Deacon <willdeacon@google.com>
This commit is contained in:
Will Deacon
2021-11-10 12:31:25 +00:00
committed by Will Deacon
parent 45f87742a6
commit c20fef387c
1 changed files with 10 additions and 1 deletions
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11
arch/arm64/kvm/hyp/pgtable.c
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@@ -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;