Starting a S2 MMU search from the beginning all the time means that we're potentially nuking a useful context (like we'd potentially have on a !VHE KVM guest).
Instead, let's always start the search from the point *after* the last allocated context. This should ensure that alternating between two EL1 contexts will not result in nuking the whole S2 each time. lookup_s2_mmu now has a chance to provide a hit. Signed-off-by: Marc Zyngier <[email protected]> --- arch/arm64/include/asm/kvm_host.h | 1 + arch/arm64/kvm/nested.c | 14 ++++++++++++-- 2 files changed, 13 insertions(+), 2 deletions(-) diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h index b71a7a237f95..b7c44adcdbf3 100644 --- a/arch/arm64/include/asm/kvm_host.h +++ b/arch/arm64/include/asm/kvm_host.h @@ -123,6 +123,7 @@ struct kvm_arch { */ struct kvm_s2_mmu *nested_mmus; size_t nested_mmus_size; + int nested_mmus_next; /* VTCR_EL2 value for this VM */ u64 vtcr; diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c index 09afafbdc8fe..214d59019935 100644 --- a/arch/arm64/kvm/nested.c +++ b/arch/arm64/kvm/nested.c @@ -363,14 +363,24 @@ static struct kvm_s2_mmu *get_s2_mmu_nested(struct kvm_vcpu *vcpu) if (s2_mmu) goto out; - for (i = 0; i < kvm->arch.nested_mmus_size; i++) { - s2_mmu = &kvm->arch.nested_mmus[i]; + /* + * Make sure we don't always search from the same point, or we + * will always reuse a potentially active context, leaving + * free contexts unused. + */ + for (i = kvm->arch.nested_mmus_next; + i < (kvm->arch.nested_mmus_size + kvm->arch.nested_mmus_next); + i++) { + s2_mmu = &kvm->arch.nested_mmus[i % kvm->arch.nested_mmus_size]; if (atomic_read(&s2_mmu->refcnt) == 0) break; } BUG_ON(atomic_read(&s2_mmu->refcnt)); /* We have struct MMUs to spare */ + /* Set the scene for the next search */ + kvm->arch.nested_mmus_next = (i + 1) % kvm->arch.nested_mmus_size; + if (kvm_s2_mmu_valid(s2_mmu)) { /* Clear the old state */ kvm_unmap_stage2_range(s2_mmu, 0, kvm_phys_size(kvm)); -- 2.20.1 _______________________________________________ kvmarm mailing list [email protected] https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
