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[34.125.139.61]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-1fed7fa4045sm17298215ad.258.2024.07.25.11.24.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 25 Jul 2024 11:24:42 -0700 (PDT) Date: Thu, 25 Jul 2024 11:24:37 -0700 From: David Matlack To: James Houghton Cc: Andrew Morton , Paolo Bonzini , Ankit Agrawal , Axel Rasmussen , Catalin Marinas , David Rientjes , James Morse , Jason Gunthorpe , Jonathan Corbet , Marc Zyngier , Oliver Upton , Raghavendra Rao Ananta , Ryan Roberts , Sean Christopherson , Shaoqin Huang , Suzuki K Poulose , Wei Xu , Will Deacon , Yu Zhao , Zenghui Yu , kvmarm@lists.linux.dev, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v6 09/11] KVM: x86: Implement fast_only versions of kvm_{test_,}age_gfn Message-ID: References: <20240724011037.3671523-1-jthoughton@google.com> <20240724011037.3671523-10-jthoughton@google.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240724011037.3671523-10-jthoughton@google.com> On 2024-07-24 01:10 AM, James Houghton wrote: > These fast-only versions simply ignore the shadow MMU. We can locklessly > handle the shadow MMU later. > > Set HAVE_KVM_MMU_NOTIFIER_YOUNG_FAST_ONLY for X86_64 only, as that is > the only case where the TDP MMU might be used. Without the TDP MMU, the > fast-only notifiers will always be no-ops. It would be ideal not to > report has_fast_only if !tdp_mmu_enabled, but tdp_mmu_enabled can be > changed at any time. tdp_mmu_enabled is a read-only KVM parameter. And even when it was writable, it was still fixed for a given VM at VM creation time. Would it make more sense to have kvm_arch_post_init_vm() set has_fast_aging if the architecture supports it. And for x86 that means iff tdp_mmu_enabled. > > Signed-off-by: James Houghton > --- > arch/x86/kvm/Kconfig | 1 + > arch/x86/kvm/mmu/mmu.c | 4 ++-- > 2 files changed, 3 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig > index 6ac43074c5e9..ed9049cf1255 100644 > --- a/arch/x86/kvm/Kconfig > +++ b/arch/x86/kvm/Kconfig > @@ -24,6 +24,7 @@ config KVM > select KVM_COMMON > select KVM_GENERIC_MMU_NOTIFIER > select KVM_MMU_NOTIFIER_YOUNG_LOCKLESS > + select HAVE_KVM_MMU_NOTIFIER_YOUNG_FAST_ONLY if X86_64 > select HAVE_KVM_IRQCHIP > select HAVE_KVM_PFNCACHE > select HAVE_KVM_DIRTY_RING_TSO > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index 919d59385f89..3c6c9442434a 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -1641,7 +1641,7 @@ bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range) > if (tdp_mmu_enabled) > young |= kvm_tdp_mmu_age_gfn_range(kvm, range); > > - if (kvm_has_shadow_mmu_sptes(kvm)) { > + if (!range->arg.fast_only && kvm_has_shadow_mmu_sptes(kvm)) { > write_lock(&kvm->mmu_lock); > young = kvm_handle_gfn_range(kvm, range, kvm_age_rmap); > write_unlock(&kvm->mmu_lock); > @@ -1657,7 +1657,7 @@ bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range) > if (tdp_mmu_enabled) > young |= kvm_tdp_mmu_test_age_gfn(kvm, range); > > - if (!young && kvm_has_shadow_mmu_sptes(kvm)) { > + if (!young && !range->arg.fast_only && kvm_has_shadow_mmu_sptes(kvm)) { > write_lock(&kvm->mmu_lock); > young = kvm_handle_gfn_range(kvm, range, kvm_test_age_rmap); > write_unlock(&kvm->mmu_lock); > -- > 2.46.0.rc1.232.g9752f9e123-goog >