| Message ID | 20190621093843.220980-41-marc.zyngier@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: arm64: ARMv8.3 Nested Virtualization support | expand |
On 6/21/19 10:38 AM, Marc Zyngier wrote: > 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 <marc.zyngier@arm.com> > --- > 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; For consistency, shouldn't nested_mmus_next be zero initialized in kvm_init_nested (arch/arm64/kvm/nested.c), like nested_mmus and nested_mmus_size? Not a big deal either way, since struct kvm is allocated using vzalloc. > really > /* 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));
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));
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 <marc.zyngier@arm.com> --- arch/arm64/include/asm/kvm_host.h | 1 + arch/arm64/kvm/nested.c | 14 ++++++++++++-- 2 files changed, 13 insertions(+), 2 deletions(-)