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[213.44.141.166]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-438904621cdsm36969035e9.27.2025.01.17.07.25.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 17 Jan 2025 07:25:48 -0800 (PST) From: Valentin Schneider To: Jann Horn 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 Subject: Re: [PATCH v4 29/30] x86/mm, mm/vmalloc: Defer flush_tlb_kernel_range() targeting NOHZ_FULL CPUs In-Reply-To: References: <20250114175143.81438-1-vschneid@redhat.com> <20250114175143.81438-30-vschneid@redhat.com> Date: Fri, 17 Jan 2025 16:25:45 +0100 Message-ID: MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: ONhKPz-Jd9miIDl6Th46eW12xUxPeaTGkVCYy0GJW_0_1737127549 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Stat-Signature: tsfmp5qp9gde9o8b4qrqngqhefbkjeh3 X-Rspam-User: X-Rspamd-Queue-Id: 60E6640014 X-Rspamd-Server: rspam03 X-HE-Tag: 1737127552-166637 X-HE-Meta: U2FsdGVkX19tQQVHb/WCKlK3eXffM/EHy/vbwdxsRg+JibFcnqzelJQbozItu/pS4fJvc9W2HoC5bor7ee4sPIWtXI0QrmqxtCk/NsDjMJKHCDfIgXOqsJVNWm7NklfgSBKoQ0fZKHxKTInRGa73rpDBfOmb+ByDKWSVXoWCRG+6Qs4bEb3vCupKGnqIqY6X9hupOqT72NoW6Fv0y/59/4nLVlJ1SxV+BBgT4nyQwnZfn/27fr89x27w/gaJkwMkC16u27PKAuC+LgWfzibn5ti3EewQgls/wYEdK8T1ZXY+W+Qs9K38zLK9SHsUEo/dt38lZAlFxBpIez+uojeXP7QMTqYVacf+inRIl7qCdT9AQ0GaElo6toMipyohowPMUl4RdAuiobgTyOOv9cGqF9YRauSmxUX58+zYAtcWYe2ZE9oWVypwqAqm0jcJybrzZg3cvGWjEWJwDBh/vzCAjqwyl//WDnVFYUQ6wO5lFwrqNCHkdvI89jjuAmWS3n3a7n0nRxQJpBDmKb3cKNkZuOV6FFWQozYOso6PV/DI0o99ElG4y/yqYoQwCOmHLMa+7Qrv3dMS69pCwnJyf35n7LetLulLEc+/YMDrwQaiUbiy9uawuBWqPFCib5ocNhoFn1U/mlRQQfY/jeCPFOFkJM5+VTW0lyppcm2bwXQkGoPOscrjqYjgO5IKGEcN9bGMld+VRNHhlhAkVSqmPOI4YtvG1f1BxIC5CMO2ECoBLqW8OEargD5yCCiwGBmQdt2IU4Iovl0MsfnOyDUpBiIxkW3DuqOVYCIyfUqJKvLf61aBouG1+vZKXcPpynORByykCTxP/9cnfM55QVaPbf3CEvuddkk2m1sgUMfoPYcnmeP5obNmMPPL4lsYH5C+AzMlS7KuVbfNtCmoz/LyRwlNbbHUIMbbjz3/YTXqdAs7CivuPaT0UhTOqnXo6vNfJA75tiTAxE/l4dZnVGPTAsV EvLSYIT4 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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 14/01/25 19:16, Jann Horn wrote: > 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 = of >> 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 vunma= p'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? I'm not sure if that would be a problem (not an mm expert, please do correct me) - looking at vmap_pages_range(), flush_cache_vmap() isn't deferred anyway. So after vmapping something, I wouldn't expect isolated CPUs to have invalid TLB entries for the newly vmapped page. However, upon vunmap'ing something, the TLB flush is deferred, and thus stale TLB entries can and will remain on isolated CPUs, up until they execute the deferred flush themselves (IOW for the entire duration of the "danger zone"). Does that make sense?