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[34.78.232.44]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43bc993abc5sm45371435e9.2.2025.03.04.07.33.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 04 Mar 2025 07:33:27 -0800 (PST) Date: Tue, 4 Mar 2025 15:33:23 +0000 From: Brendan Jackman To: Borislav Petkov Cc: Dave Hansen , Rik van Riel , x86@kernel.org, linux-kernel@vger.kernel.org, peterz@infradead.org, dave.hansen@linux.intel.com, zhengqi.arch@bytedance.com, nadav.amit@gmail.com, thomas.lendacky@amd.com, kernel-team@meta.com, linux-mm@kvack.org, akpm@linux-foundation.org, jannh@google.com, mhklinux@outlook.com, andrew.cooper3@citrix.com, Manali.Shukla@amd.com, mingo@kernel.org Subject: Re: [PATCH v14 11/13] x86/mm: do targeted broadcast flushing from tlbbatch code Message-ID: References: <20250226030129.530345-1-riel@surriel.com> <20250226030129.530345-12-riel@surriel.com> <20250303114618.GBZ8WWihMDjf-oy8P0@fat_crate.local> <7e1ca8c7-6f3e-44dc-9dd8-bd273a03a83e@intel.com> <20250304141134.GIZ8cKFom3W0ChHiXk@fat_crate.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250304141134.GIZ8cKFom3W0ChHiXk@fat_crate.local> X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 82B7D80012 X-Stat-Signature: s3hemrwyshe1ttytnefpdg9j8ht3onj6 X-HE-Tag: 1741102410-126485 X-HE-Meta: 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 8hdgcqVp c/yVRVcN8TTD6cUFaBEWtBq48V5902yRIUa9C6f8LMWGu8dqBpSaLbqeDuBsQf+rA1gRU48c+9qJgMN7N/ZMUA8R1b6TsFs2cOofdsCBfADYCKMe8miWGU+1tup/EiOhgvX3lo8xB/Qf4u5bQj+xhRcudzu2RIOV/6BKOD9RnCWRNR2dJiQi4mCLcSn3Ei1hRoYfXT2gySnXoN1PneMJPOolyeB0tYfjEKJnpoHzOEy8868xQ8on43/M4ZT6UJvkpcUJse1+uJju3WEW0iKlVSCJfJeAH5C/+34JKyeZqQnySCRQmQx/kfHlLetcCF9LOvosT8rGIZcRNrLIqeuH94Jh4+Sd1BVcHf4daanctz/pfY0pT+tZ5dzmO81Ako0H9oSYMnS+hlYiWXFV5bYwAhPDk6sxo2xNl3WJh8dCsxZ2T6rBrcKUTpoH91YONbpeHW8cR5cKsWIuKNa1LrBY4bfQIF5/6z1eSa2Sm 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 Tue, Mar 04, 2025 at 03:11:34PM +0100, Borislav Petkov wrote: > On Tue, Mar 04, 2025 at 12:52:47PM +0000, Brendan Jackman wrote: > > https://lore.kernel.org/all/CA+i-1C31TrceZiizC_tng_cc-zcvKsfXLAZD_XDftXnp9B2Tdw@mail.gmail.com/ > > Lemme try to understand what you're suggesting on that subthread: > > > static inline void arch_start_context_switch(struct task_struct *prev) > > { > > arch_paravirt_start_context_switch(prev); > > tlb_start_context_switch(prev); > > } > > This kinda makes sense to me... Yeah so basically my concern here is that we are doing something that's about context switching, but we're doing it in mm-switching code, entangling an assumption that "context_switch() must either call this function or that function". Whereas if we just call it explicitly from context_switch() it will be much clearer. > > Now I think about it... if we always tlbsync() before a context switch, is the > > cant_migrate() above actually required? I think with that, even if we migrated > > in the middle of e.g. broadcast_kernel_range_flush(), we'd be fine? (At > > least, from the specific perspective of the invplgb code, presumably having > > preemption on there would break things horribly in other ways). > > I think we still need it because you need to TLBSYNC on the same CPU you've > issued the INVLPGB and actually, you want all TLBs to have been synched > system-wide. > > Or am I misunderstanding it? Er, I might be exposing my own ignorance here. I was thinking that you always go through context_switch() before you get migrated, but I might not understand hwo migration happens.