From: Marc Zyngier <maz@kernel.org> To: Jing Zhang <jingzhangos@google.com> Cc: KVM <kvm@vger.kernel.org>, KVMARM <kvmarm@lists.cs.columbia.edu>, Will Deacon <will@kernel.org>, Paolo Bonzini <pbonzini@redhat.com>, David Matlack <dmatlack@google.com>, Oliver Upton <oupton@google.com>, Reiji Watanabe <reijiw@google.com>, Ricardo Koller <ricarkol@google.com>, Raghavendra Rao Ananta <rananta@google.com> Subject: Re: [PATCH v1 2/3] KVM: arm64: Add fast path to handle permission relaxation during dirty logging Date: Sun, 16 Jan 2022 11:14:46 +0000 [thread overview] Message-ID: <87wnj0x789.wl-maz@kernel.org> (raw) In-Reply-To: <20220113221829.2785604-3-jingzhangos@google.com> On Thu, 13 Jan 2022 22:18:28 +0000, Jing Zhang <jingzhangos@google.com> wrote: > > To reduce MMU lock contention during dirty logging, all permission > relaxation operations would be performed under read lock. > > Signed-off-by: Jing Zhang <jingzhangos@google.com> > --- > arch/arm64/kvm/mmu.c | 20 ++++++++++++++++++-- > 1 file changed, 18 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > index cafd5813c949..15393cb61a3f 100644 > --- a/arch/arm64/kvm/mmu.c > +++ b/arch/arm64/kvm/mmu.c > @@ -1084,6 +1084,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > unsigned long vma_pagesize, fault_granule; > enum kvm_pgtable_prot prot = KVM_PGTABLE_PROT_R; > struct kvm_pgtable *pgt; > + bool use_mmu_readlock = false; Group this with the rest of the flags. It would also be better if it described the condition this represent rather than what we use it for. For example, 'perm_fault_while_logging', or something along those lines. > > fault_granule = 1UL << ARM64_HW_PGTABLE_LEVEL_SHIFT(fault_level); > write_fault = kvm_is_write_fault(vcpu); > @@ -1212,7 +1213,19 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > if (exec_fault && device) > return -ENOEXEC; > > - write_lock(&kvm->mmu_lock); > + if (fault_status == FSC_PERM && fault_granule == PAGE_SIZE > + && logging_active && write_fault) > + use_mmu_readlock = true; This looks a bit clumsy, and would be better if this was kept together with the rest of the logging_active==true code. Something like: diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c index bc2aba953299..59b1d5f46b06 100644 --- a/arch/arm64/kvm/mmu.c +++ b/arch/arm64/kvm/mmu.c @@ -1114,6 +1114,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, if (logging_active) { force_pte = true; vma_shift = PAGE_SHIFT; + use_readlock = (fault_status == FSC_PERM && write_fault); } else { vma_shift = get_vma_page_shift(vma, hva); } I don't think we have to check for fault_granule here, as I don't see how you could get a permission fault for something other than a page size mapping. > + /* > + * To reduce MMU contentions and enhance concurrency during dirty > + * logging dirty logging, only acquire read lock for permission > + * relaxation. This fast path would greatly reduce the performance > + * degradation of guest workloads. > + */ This comment makes more sense with the previous hunk. Drop the last sentence though, as it doesn't bring much information. > + if (use_mmu_readlock) > + read_lock(&kvm->mmu_lock); > + else > + write_lock(&kvm->mmu_lock); > pgt = vcpu->arch.hw_mmu->pgt; > if (mmu_notifier_retry(kvm, mmu_seq)) > goto out_unlock; > @@ -1271,7 +1284,10 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > } > > out_unlock: > - write_unlock(&kvm->mmu_lock); > + if (use_mmu_readlock) > + read_unlock(&kvm->mmu_lock); > + else > + write_unlock(&kvm->mmu_lock); > kvm_set_pfn_accessed(pfn); > kvm_release_pfn_clean(pfn); > return ret != -EAGAIN ? ret : 0; Thanks, M. -- Without deviation from the norm, progress is not possible.
WARNING: multiple messages have this Message-ID (diff)
From: Marc Zyngier <maz@kernel.org> To: Jing Zhang <jingzhangos@google.com> Cc: KVM <kvm@vger.kernel.org>, David Matlack <dmatlack@google.com>, Paolo Bonzini <pbonzini@redhat.com>, Will Deacon <will@kernel.org>, KVMARM <kvmarm@lists.cs.columbia.edu> Subject: Re: [PATCH v1 2/3] KVM: arm64: Add fast path to handle permission relaxation during dirty logging Date: Sun, 16 Jan 2022 11:14:46 +0000 [thread overview] Message-ID: <87wnj0x789.wl-maz@kernel.org> (raw) In-Reply-To: <20220113221829.2785604-3-jingzhangos@google.com> On Thu, 13 Jan 2022 22:18:28 +0000, Jing Zhang <jingzhangos@google.com> wrote: > > To reduce MMU lock contention during dirty logging, all permission > relaxation operations would be performed under read lock. > > Signed-off-by: Jing Zhang <jingzhangos@google.com> > --- > arch/arm64/kvm/mmu.c | 20 ++++++++++++++++++-- > 1 file changed, 18 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > index cafd5813c949..15393cb61a3f 100644 > --- a/arch/arm64/kvm/mmu.c > +++ b/arch/arm64/kvm/mmu.c > @@ -1084,6 +1084,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > unsigned long vma_pagesize, fault_granule; > enum kvm_pgtable_prot prot = KVM_PGTABLE_PROT_R; > struct kvm_pgtable *pgt; > + bool use_mmu_readlock = false; Group this with the rest of the flags. It would also be better if it described the condition this represent rather than what we use it for. For example, 'perm_fault_while_logging', or something along those lines. > > fault_granule = 1UL << ARM64_HW_PGTABLE_LEVEL_SHIFT(fault_level); > write_fault = kvm_is_write_fault(vcpu); > @@ -1212,7 +1213,19 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > if (exec_fault && device) > return -ENOEXEC; > > - write_lock(&kvm->mmu_lock); > + if (fault_status == FSC_PERM && fault_granule == PAGE_SIZE > + && logging_active && write_fault) > + use_mmu_readlock = true; This looks a bit clumsy, and would be better if this was kept together with the rest of the logging_active==true code. Something like: diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c index bc2aba953299..59b1d5f46b06 100644 --- a/arch/arm64/kvm/mmu.c +++ b/arch/arm64/kvm/mmu.c @@ -1114,6 +1114,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, if (logging_active) { force_pte = true; vma_shift = PAGE_SHIFT; + use_readlock = (fault_status == FSC_PERM && write_fault); } else { vma_shift = get_vma_page_shift(vma, hva); } I don't think we have to check for fault_granule here, as I don't see how you could get a permission fault for something other than a page size mapping. > + /* > + * To reduce MMU contentions and enhance concurrency during dirty > + * logging dirty logging, only acquire read lock for permission > + * relaxation. This fast path would greatly reduce the performance > + * degradation of guest workloads. > + */ This comment makes more sense with the previous hunk. Drop the last sentence though, as it doesn't bring much information. > + if (use_mmu_readlock) > + read_lock(&kvm->mmu_lock); > + else > + write_lock(&kvm->mmu_lock); > pgt = vcpu->arch.hw_mmu->pgt; > if (mmu_notifier_retry(kvm, mmu_seq)) > goto out_unlock; > @@ -1271,7 +1284,10 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > } > > out_unlock: > - write_unlock(&kvm->mmu_lock); > + if (use_mmu_readlock) > + read_unlock(&kvm->mmu_lock); > + else > + write_unlock(&kvm->mmu_lock); > kvm_set_pfn_accessed(pfn); > kvm_release_pfn_clean(pfn); > return ret != -EAGAIN ? ret : 0; Thanks, M. -- Without deviation from the norm, progress is not possible. _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
next prev parent reply other threads:[~2022-01-16 11:14 UTC|newest] Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-01-13 22:18 [PATCH v1 0/3] ARM64: Guest performance improvement during dirty Jing Zhang 2022-01-13 22:18 ` Jing Zhang 2022-01-13 22:18 ` [PATCH v1 1/3] KVM: arm64: Use read/write spin lock for MMU protection Jing Zhang 2022-01-13 22:18 ` Jing Zhang 2022-01-13 22:18 ` [PATCH v1 2/3] KVM: arm64: Add fast path to handle permission relaxation during dirty logging Jing Zhang 2022-01-13 22:18 ` Jing Zhang 2022-01-16 11:14 ` Marc Zyngier [this message] 2022-01-16 11:14 ` Marc Zyngier 2022-01-17 3:23 ` Jing Zhang 2022-01-17 3:23 ` Jing Zhang 2022-01-13 22:18 ` [PATCH v1 3/3] KVM: selftests: Add vgic initialization for dirty log perf test for ARM Jing Zhang 2022-01-13 22:18 ` Jing Zhang
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