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[2003:cb:c730:f600:afa2:4e8a:448a:9831]) by smtp.gmail.com with ESMTPSA id m38-20020a05600c3b2600b00417fdf4677asm2977868wms.14.2024.04.12.13.01.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 12 Apr 2024 13:01:05 -0700 (PDT) Message-ID: <5ed763c2-7e01-4c31-923c-ba62f0d0e993@redhat.com> Date: Fri, 12 Apr 2024 22:01:03 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/4] KVM: delete .change_pte MMU notifier callback To: Paolo Bonzini , Peter Xu Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Marc Zyngier , Oliver Upton , Tianrui Zhao , Bibo Mao , Thomas Bogendoerfer , Nicholas Piggin , Anup Patel , Atish Patra , Sean Christopherson , Andrew Morton , 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, Andrea Arcangeli References: <20240405115815.3226315-1-pbonzini@redhat.com> <20240405115815.3226315-2-pbonzini@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Stat-Signature: nc63u9jau6kfi69h98ook7d171dibr9t X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 9793FC000E X-HE-Tag: 1712952072-292387 X-HE-Meta: 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 OcYJDvTa 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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 11.04.24 18:55, Paolo Bonzini wrote: > On Mon, Apr 8, 2024 at 3:56 PM Peter Xu wrote: >> Paolo, >> >> I may miss a bunch of details here (as I still remember some change_pte >> patches previously on the list..), however not sure whether we considered >> enable it? Asked because I remember Andrea used to have a custom tree >> maintaining that part: >> >> https://github.com/aagit/aa/commit/c761078df7a77d13ddfaeebe56a0f4bc128b1968 > > The patch enables it only for KSM, so it would still require a bunch > of cleanups, for example I also would still use set_pte_at() in all > the places that are not KSM. This would at least fix the issue with > the poor documentation of where to use set_pte_at_notify() vs > set_pte_at(). > > With regard to the implementation, I like the idea of disabling the > invalidation on the MMU notifier side, but I would rather have > MMU_NOTIFIER_CHANGE_PTE as a separate field in the range instead of > overloading the event field. > >> Maybe it can't be enabled for some reason that I overlooked in the current >> tree, or we just decided to not to? > > I have just learnt about the patch, nobody had ever mentioned it even > though it's almost 2 years old... It's a lot of code though and no one I assume Andrea used it on his tree where he also has a version of "randprotect" (even included in that commit subject) to mitigate a KSM security issue that was reported by some security researchers [1] a while ago. From what I recall, the industry did not end up caring about that security issue that much. IIUC, with "randprotect" we get a lot more R/O protection even when not de-duplicating a page -- thus the name. Likely, the reporter mentioned in the commit is a researcher that played with Andreas fix for the security issue. But I'm just speculating at this point :) > has ever reported an issue for over 10 years, so I think it's easiest > to just rip the code out. Yes. Can always be readded in a possibly cleaner fashion (like you note above), when deemed necessary and we are willing to support it. [1] https://gruss.cc/files/remote_dedup.pdf -- Cheers, David / dhildenb