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[213.44.141.166]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43993847f39sm32922065e9.14.2025.02.18.14.40.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 18 Feb 2025 14:40:34 -0800 (PST) From: Valentin Schneider To: Dave Hansen , 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: <352317e3-c7dc-43b4-b4cb-9644489318d0@intel.com> References: <20250114175143.81438-1-vschneid@redhat.com> <20250114175143.81438-30-vschneid@redhat.com> <352317e3-c7dc-43b4-b4cb-9644489318d0@intel.com> Date: Tue, 18 Feb 2025 23:40:31 +0100 Message-ID: MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 7Ep2USrCAMPcr6NngY8UTr2Nt-4tVQuW3-KmKTsXUEY_1739918436 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 6C63212000D X-Stat-Signature: 9em8mujqsorfj5fskjgekoi417gqsez5 X-Rspam-User: X-HE-Tag: 1739918439-340968 X-HE-Meta: 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 Zs6GV+Ln y6uOGo9AXaHuAPAW0OPro8+cqFdShd+ow881G8K09hAmd+OgRi2Fa0rWbh4Ef+VssHwjdljXq8j2OXVKiGyltX8+Jr6xGSzQJHLV2DFpPz+hRPle31GZNdGkXmPuBeeR1dQus35lioWtAsUrwLR/4XthR72Kon+BsTzypxTM2wbCXVzLERHY4rD/QtFLnkIZ0qHFsCRlmfzVfCZl870nvSvoTDDcRq3ObTrofDF4aZoVoFfbSBsawgsj9zCVYP9m0FYFvE7gT5MhZBXIxN2R5hslYWIBMQ79xOAg3nGEw2KPVBY9I385aBybFbrWweOYUWB6eGSHXx735II5gnjJMBUjIqqHpf/UG/Xze/Y9dfNtbzTce5ikyjdlKlBFCD16eCWKM40u6Sa5iFNz/CTvU+Jw0dXxQ+Y4YFGOzxLxpShOxTg8= 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 11/02/25 06:22, Dave Hansen wrote: > On 2/11/25 05:33, Valentin Schneider wrote: >>> 2. It's wrong to assume that TLB entries are only populated for >>> addresses you access - thanks to speculative execution, you have to >>> assume that the CPU might be populating random TLB entries all over >>> the place. >> Gotta love speculation. Now it is supposed to be limited to genuinely >> accessible data & code, right? Say theoretically we have a full TLBi as >> literally the last thing before doing the return-to-userspace, speculation >> should be limited to executing maybe bits of the return-from-userspace >> code? > > In practice, it's mostly limited like that. > > Architecturally, there are no promises from the CPU. It is within its > rights to cache anything from the page tables at any time. If it's in > the CR3 tree, it's fair game. > So what if the VMEMMAP range *isn't* in the CR3 tree when a CPU is executing in userspace? AIUI that's the case with kPTI - the remaining kernel pages should mostly be .entry.text and cpu_entry_area, at least for x86. It sounds like it wouldn't do much for arm64 though, if with CnP a CPU executing in userspace and with the user/trampoline page table installed can still use TLB entries of another CPU executing in kernelspace with the kernel page table installed.