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[213.44.141.166]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4395a0558e2sm247191865e9.11.2025.02.20.09.10.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 20 Feb 2025 09:10:17 -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: References: <20250114175143.81438-1-vschneid@redhat.com> <20250114175143.81438-30-vschneid@redhat.com> <352317e3-c7dc-43b4-b4cb-9644489318d0@intel.com> Date: Thu, 20 Feb 2025 18:10:15 +0100 Message-ID: MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 4af6EuA-_KcjalzQI23CGvgXN30w0_mFP1nQEoKktxo_1740071419 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Rspamd-Queue-Id: 644EE1C0015 X-Stat-Signature: 759ijuz1yhmdcdh8ypdm4twasge1djti X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1740071424-554179 X-HE-Meta: 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 wTQ337QX 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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 19/02/25 12:25, Dave Hansen wrote: > On 2/19/25 07:13, Valentin Schneider wrote: >>> Maybe I missed part of the discussion though. Is VMEMMAP your only >>> concern? I would have guessed that the more generic vmalloc() >>> functionality would be harder to pin down. >> Urgh, that'll teach me to send emails that late - I did indeed mean the >> vmalloc() range, not at all VMEMMAP. IIUC *neither* are present in the user >> kPTI page table and AFAICT the page table swap is done before the actual vmap'd >> stack (CONFIG_VMAP_STACK=y) gets used. > > OK, so rewriting your question... ;) > >> So what if the vmalloc() range *isn't* in the CR3 tree when a CPU is >> executing in userspace? > > The LDT and maybe the PEBS buffers are the only implicit supervisor > accesses to vmalloc()'d memory that I can think of. But those are both > handled specially and shouldn't ever get zapped while in use. The LDT > replacement has its own IPIs separate from TLB flushing. > > But I'm actually not all that worried about accesses while actually > running userspace. It's that "danger zone" in the kernel between entry > and when the TLB might have dangerous garbage in it. > So say we have kPTI, thus no vmalloc() mapped in CR3 when running userspace, and do a full TLB flush right before switching to userspace - could the TLB still end up with vmalloc()-range-related entries when we're back in the kernel and going through the danger zone? > BTW, I hope this whole thing is turned off on 32-bit. There, we can > actually take and handle faults on the vmalloc() area. If you get one of > those faults in your "danger zone", it'll start running page fault code > which will branch out to god-knows-where and certainly isn't noinstr. Sounds... Fun. Thanks for pointing out the landmines.