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AJvYcCWOxmTVEuipjvAZW436f6pdXFKKFYkD8te4JSOkGaBsWZq/hEJ2bFXehDz3ug0JBpdEe4KqIf6cX18T3a61vne6ZJY= X-Gm-Message-State: AOJu0YwfMezUKypHHfJjN/LCrEelcWyhFYgM4b7nNfxFXHp4oe3HI0PJ FCDqcO0asxPEx/OdCh+cWO0+YEWsQLrc8oRdJe2DZor7Q3bYW8OKTIkZjCYMnHgXmnYYDtXLDTJ 85Q== X-Google-Smtp-Source: AGHT+IE8CrGE6yHurBu6oRRUdhNStzcxsQMqGws9O1toyt+VIrjo1lbnGIr3E72VqB9zErBllk+K4v4iLAw= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a05:6a00:2d94:b0:6ed:95ce:3417 with SMTP id fb20-20020a056a002d9400b006ed95ce3417mr191844pfb.5.1712933663717; Fri, 12 Apr 2024 07:54:23 -0700 (PDT) Date: Fri, 12 Apr 2024 07:54:22 -0700 In-Reply-To: <86jzl2sovz.wl-maz@kernel.org> Mime-Version: 1.0 References: <20240405115815.3226315-1-pbonzini@redhat.com> <20240405115815.3226315-2-pbonzini@redhat.com> <20240412104408.GA27645@willie-the-truck> <86jzl2sovz.wl-maz@kernel.org> Message-ID: Subject: Re: [PATCH 1/4] KVM: delete .change_pte MMU notifier callback From: Sean Christopherson To: Marc Zyngier Cc: Will Deacon , Paolo Bonzini , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Oliver Upton , Tianrui Zhao , Bibo Mao , Thomas Bogendoerfer , Nicholas Piggin , Anup Patel , Atish Patra , Andrew Morton , David Hildenbrand , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, kvm-riscv@lists.infradead.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org Content-Type: text/plain; charset="us-ascii" X-Rspamd-Queue-Id: 0280520005 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: om9g15x6nksbhztfpdnqh69hm6khenxd X-HE-Tag: 1712933664-796011 X-HE-Meta: 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 jOmK8nyV 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Apr 12, 2024, Marc Zyngier wrote: > On Fri, 12 Apr 2024 11:44:09 +0100, Will Deacon wrote: > > On Fri, Apr 05, 2024 at 07:58:12AM -0400, Paolo Bonzini wrote: > > Also, if you're in the business of hacking the MMU notifier code, it > > would be really great to change the .clear_flush_young() callback so > > that the architecture could handle the TLB invalidation. At the moment, > > the core KVM code invalidates the whole VMID courtesy of 'flush_on_ret' > > being set by kvm_handle_hva_range(), whereas we could do a much > > lighter-weight and targetted TLBI in the architecture page-table code > > when we actually update the ptes for small ranges. > > Indeed, and I was looking at this earlier this week as it has a pretty > devastating effect with NV (it blows the shadow S2 for that VMID, with > costly consequences). > > In general, it feels like the TLB invalidation should stay with the > code that deals with the page tables, as it has a pretty good idea of > what needs to be invalidated and how -- specially on architectures > that have a HW-broadcast facility like arm64. Would this be roughly on par with an in-line flush on arm64? The simpler, more straightforward solution would be to let architectures override flush_on_ret, but I would prefer something like the below as x86 can also utilize a range-based flush when running as a nested hypervisor. diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index ff0a20565f90..b65116294efe 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -601,6 +601,7 @@ static __always_inline kvm_mn_ret_t __kvm_handle_hva_range(struct kvm *kvm, struct kvm_gfn_range gfn_range; struct kvm_memory_slot *slot; struct kvm_memslots *slots; + bool need_flush = false; int i, idx; if (WARN_ON_ONCE(range->end <= range->start)) @@ -653,10 +654,22 @@ static __always_inline kvm_mn_ret_t __kvm_handle_hva_range(struct kvm *kvm, break; } r.ret |= range->handler(kvm, &gfn_range); + + /* + * Use a precise gfn-based TLB flush when possible, as + * most mmu_notifier events affect a small-ish range. + * Fall back to a full TLB flush if the gfn-based flush + * fails, and don't bother trying the gfn-based flush + * if a full flush is already pending. + */ + if (range->flush_on_ret && !need_flush && r.ret && + kvm_arch_flush_remote_tlbs_range(kvm, gfn_range.start + gfn_range.end - gfn_range.start + 1)) + need_flush = true; } } - if (range->flush_on_ret && r.ret) + if (need_flush) kvm_flush_remote_tlbs(kvm); if (r.found_memslot)