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AJvYcCUX3QUG/GeNeE94nZv6UrWu4kYVWNunCodK26EoFArLZY1Sh9zzKOCVAal7wTA9YWSIJ91yIiP8Cw==@kvack.org X-Gm-Message-State: AOJu0Yz6f55UwACnD438dW8+69f/QvDCCCJ9TSt7NhzzSjxHu7lLdPML lopBqym7HuRNTjfBNYizbqa8DfyodqUGeTV2bFla+jyCatC4KtvecMZ7P+YXZ4dEozFf1yuVDi4 tKkIXF+rqoK++mOHr2diXruZpyZiexeI3NCM4 X-Gm-Gg: ASbGncv7i+yzYI4dsJNFvzfFcmEwUd3AZvoHx2L39qqeWZTNb8HXd1dFfrOe0IAKAzu 12XL/GPKGry2RGQAo7FNKDWalgm67dd51gnWnB82ZLoiXGGrb91DsqMAhA8FYYWiZaQ== X-Google-Smtp-Source: AGHT+IFOWOuSvDhgzEqoKb2CNkVmA/sXHofQ9hZDfWF+l4vbbQk0RN2k51cQSZIijLzKAw1RUyxlH5Nb9O1wedqOjko= X-Received: by 2002:a50:d4d2:0:b0:5d1:22e1:7458 with SMTP id 4fb4d7f45d1cf-5d9f695dda7mr124694a12.4.1736878640478; Tue, 14 Jan 2025 10:17:20 -0800 (PST) MIME-Version: 1.0 References: <20250114175143.81438-1-vschneid@redhat.com> <20250114175143.81438-30-vschneid@redhat.com> In-Reply-To: <20250114175143.81438-30-vschneid@redhat.com> From: Jann Horn Date: Tue, 14 Jan 2025 19:16:44 +0100 X-Gm-Features: AbW1kvY7dNxOnvBqE7JSPz560QoJfBjiwfsZgS18MpZMQ07ZRC1TBr6Zwl5A-60 Message-ID: Subject: Re: [PATCH v4 29/30] x86/mm, mm/vmalloc: Defer flush_tlb_kernel_range() targeting NOHZ_FULL CPUs To: Valentin Schneider Cc: linux-kernel@vger.kernel.org, x86@kernel.org, virtualization@lists.linux.dev, linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev, linux-riscv@lists.infradead.org, linux-perf-users@vger.kernel.org, xen-devel@lists.xenproject.org, kvm@vger.kernel.org, linux-arch@vger.kernel.org, rcu@vger.kernel.org, linux-hardening@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, bpf@vger.kernel.org, bcm-kernel-feedback-list@broadcom.com, Juergen Gross , Ajay Kaher , Alexey Makhalov , Russell King , Catalin Marinas , Will Deacon , Huacai Chen , WANG Xuerui , Paul Walmsley , Palmer Dabbelt , Albert Ou , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Peter Zijlstra , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , "Liang, Kan" , Boris Ostrovsky , Josh Poimboeuf , Pawan Gupta , Sean Christopherson , Paolo Bonzini , Andy Lutomirski , Arnd Bergmann , Frederic Weisbecker , "Paul E. McKenney" , Jason Baron , Steven Rostedt , Ard Biesheuvel , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Uladzislau Rezki , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Juri Lelli , Clark Williams , Yair Podemsky , Tomas Glozar , Vincent Guittot , Dietmar Eggemann , Ben Segall , Mel Gorman , Kees Cook , Andrew Morton , Christoph Hellwig , Shuah Khan , Sami Tolvanen , Miguel Ojeda , Alice Ryhl , "Mike Rapoport (Microsoft)" , Samuel Holland , Rong Xu , Nicolas Saenz Julienne , Geert Uytterhoeven , Yosry Ahmed , "Kirill A. Shutemov" , "Masami Hiramatsu (Google)" , Jinghao Jia , Luis Chamberlain , Randy Dunlap , Tiezhu Yang Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: exsmkgsnmpzc8wyx9bdmiizt7jgdj6n7 X-Rspam-User: X-Rspamd-Queue-Id: 8013B100007 X-Rspamd-Server: rspam08 X-HE-Tag: 1736878642-338136 X-HE-Meta: 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 NRBELCZq +4xFk1f3pnr0+E/CPwkI0JEwAV2S1yJzUOfse0T6SNkAqHk6tMN2rwrQ4yn/4XlgSzKvvNQ6rQ+dsFea7zvhiGslvjeGyL1EdslqbBoBbwhw1Jk5dQz7MOvEG0w1QP+F7ohU90wNmzLHZlgJOAAE8lZjxgzZdTLUczDVEuf6pytW32m5IP/lVUl7+qZKPrxFUak/bPl39AtqTi693I9e9mwCrM501QVe4i89uDBNYzJ4y9BEEbxhrAmkWmNloMd/WCl2/BE/rD8HUxe9MrT6qWlC2ZqpHnmAjkZGbnVbVyg1rcUnyRynLUUU3W2T+kl48ZtPG X-Bogosity: Ham, tests=bogofilter, spamicity=0.000002, 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 Tue, Jan 14, 2025 at 6:51=E2=80=AFPM Valentin Schneider wrote: > vunmap()'s issued from housekeeping CPUs are a relatively common source o= f > interference for isolated NOHZ_FULL CPUs, as they are hit by the > flush_tlb_kernel_range() IPIs. > > Given that CPUs executing in userspace do not access data in the vmalloc > range, these IPIs could be deferred until their next kernel entry. > > Deferral vs early entry danger zone > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > > This requires a guarantee that nothing in the vmalloc range can be vunmap= 'd > and then accessed in early entry code. In other words, it needs a guarantee that no vmalloc allocations that have been created in the vmalloc region while the CPU was idle can then be accessed during early entry, right?