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AJvYcCV+O27cGHNoMrc/SxqHvcXFNSaGYLjFo0ORdmVB3wzpn3mjiVSmq+S5Np1Zcv7y4d5g5j6xmj2tXBWZ29bz2dc0mGk= X-Gm-Message-State: AOJu0Yw9x+mkARHER9Ue0/pQGKfnjXqhvFDZD9YLUCTVkqGLTCYzXFd1 kGp9Z63cFucA7N/xunvOoeX06LKdXOe0NfODLQSAHehlvHYHCKhAQQYq/nMsvLpSDRE41aDvFu0 F7Q== X-Google-Smtp-Source: AGHT+IGA4ztkhkZCfS7682EU3T6gUsIsEcYhQEyC6yG3styg4+lnibMOlTTY3gI+fKNitZWoNIXkz2MBC8E= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a05:6a00:9399:b0:6ec:f266:d214 with SMTP id ka25-20020a056a00939900b006ecf266d214mr254346pfb.4.1713200632756; Mon, 15 Apr 2024 10:03:52 -0700 (PDT) Date: Mon, 15 Apr 2024 10:03:51 -0700 In-Reply-To: <86h6g5si0m.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> <86h6g5si0m.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-Server: rspam08 X-Rspamd-Queue-Id: 1D4BC100007 X-Stat-Signature: wifbr4j1zbqzku5mh684gdu914kwj6d3 X-Rspam-User: X-HE-Tag: 1713200633-891816 X-HE-Meta: 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 afqjyJr+ 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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 Sat, Apr 13, 2024, Marc Zyngier wrote: > On Fri, 12 Apr 2024 15:54:22 +0100, Sean Christopherson wrote: > > > > 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. ... > I think this works for us on HW that has range invalidation, which > would already be a positive move. > > For the lesser HW that isn't range capable, it also gives the > opportunity to perform the iteration ourselves or go for the nuclear > option if the range is larger than some arbitrary constant (though > this is additional work). > > But this still considers the whole range as being affected by > range->handler(). It'd be interesting to try and see whether more > precise tracking is (or isn't) generally beneficial. I assume the idea would be to let arch code do single-page invalidations of stage-2 entries for each gfn? Unless I'm having a brain fart, x86 can't make use of that functionality. Intel doesn't provide any way to do targeted invalidation of stage-2 mappings. AMD provides an instruction to do broadcast invalidations, but it takes a virtual address, i.e. a stage-1 address. I can't tell if it's a host virtual address or a guest virtual address, but it's a moot point because KVM doen't have the guest virtual address, and if it's a host virtual address, there would need to be valid mappings in the host page tables for it to work, which KVM can't guarantee.