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Mon, 20 Jan 2025 10:57:10 -0800 (PST) Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3826.300.87.4.3\)) Subject: Re: [PATCH v5 10/12] x86,tlb: do targeted broadcast flushing from tlbbatch code From: Nadav Amit In-Reply-To: <11fcbbbb545576a1bfa54839cf87a72faf5603ab.camel@surriel.com> Date: Mon, 20 Jan 2025 20:56:57 +0200 Cc: the arch/x86 maintainers , Linux Kernel Mailing List , Borislav Petkov , peterz@infradead.org, Dave Hansen , zhengqi.arch@bytedance.com, thomas.lendacky@amd.com, kernel-team@meta.com, "open list:MEMORY MANAGEMENT" , Andrew Morton , jannh@google.com, mhklinux@outlook.com, andrew.cooper3@citrix.com Content-Transfer-Encoding: 7bit Message-Id: <5501C6EC-38C7-472F-B129-F7A5144C3096@gmail.com> References: <20250116023127.1531583-1-riel@surriel.com> <20250116023127.1531583-11-riel@surriel.com> <13bc0c49-09a4-434e-bd35-1ea50be38e25@gmail.com> <4dcf2b4ecaede883e2c7f6af3db58a4f6afaf4ad.camel@surriel.com> <2975f6a4-58ef-4499-b177-4b73ead4c670@gmail.com> <2c93b3f17e658483e3ea03ca3f0a717668fd117d.camel@surriel.com> <11d9f41a-eae3-43a1-90bc-eb5c69020002@gmail.com> <5F51AFA6-EA48-42BF-8E24-10FAAAA7BE4B@gmail.com> <11fcbbbb545576a1bfa54839cf87a72faf5603ab.camel@surriel.com> To: Rik van Riel X-Mailer: Apple Mail (2.3826.300.87.4.3) X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 9D2BC40003 X-Stat-Signature: e3ws59b6p4r55jjixr33mrbdi464uhsp X-Rspam-User: X-HE-Tag: 1737399433-777476 X-HE-Meta: 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 /Gs02P8l MWzj5mRQ0RpGMP4c5gtXgFDE8fqaozhINpwpu6bueEi7HzcrZYwD/3CHBcwS9NriWJCE6gp5KlA03Jp8cmSrlKEfU8NcsFc+xhJoAuPY+TywfYooUsIUTmzu2vRpgbiwXOkTNQR4aGfonW/BdWzVWp7T32qJQ5/jLJ2XQYFIMIqABXEBpa2HFff5BgFkt5higGfqvPyQVW+9+afsugw4T+X/ipvjnt7m21q/MK48FtUOFBptMYBh15M/UzbMrtsAEaEZ5OA2dc5mpUz1pUV5H7UKbpE0A658PPRv5asaW0YQp1UQZHp+XVPO97Mhaib9J3nse4S0s1m5pFiZEXQ0360VJ/1+rsMiuBO+BCekvwSE8MTnBZzT9dV/ENs+fGT+Gt+5PQDb4lzabtoElPjDmELBtqnC/5Hk2D+ADX6Ap2IBce/zWZPZi3Y0G2gKcM5mFugAdMkR/0VXbNs11aVoM+80T+YZKNtGN/ht2 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 20 Jan 2025, at 19:56, Rik van Riel wrote: > > How would you keep track of CPUs where the tlbsync > has NOT happened before arch_tlbbatch_flush()? > > That part seems to be missing still. You only keep track if there is a pending tlbsync on *your* CPU. No need to track if other CPUs did not issue tlbsync during arch_tlbbatch_add_pending(). If the process that does the reclamation was migrated, a TLBSYNC is issued during the context switch, before that thread that does the reclamation has any chance of being scheduled. I hope this code changes on top of your would make it clearer: > +void arch_tlbbatch_add_pending(struct arch_tlbflush_unmap_batch *batch, > + struct mm_struct *mm, > + unsigned long uaddr) > +{ > + if (static_cpu_has(X86_FEATURE_INVLPGB) && mm_global_asid(mm)) { > + u16 asid = mm_global_asid(mm); > + /* > + * Queue up an asynchronous invalidation. The corresponding > + * TLBSYNC is done in arch_tlbbatch_flush(), and must be done > + * on the same CPU. > + */ #if 0 // remove > + if (!batch->used_invlpgb) { > + batch->used_invlpgb = true; > + migrate_disable(); > + } #endif batch->used_invlpg = true; preempt_disable(); > + invlpgb_flush_user_nr_nosync(kern_pcid(asid), uaddr, 1, false); > + /* Do any CPUs supporting INVLPGB need PTI? */ > + if (static_cpu_has(X86_FEATURE_PTI)) > + invlpgb_flush_user_nr_nosync(user_pcid(asid), uaddr, 1, false); this_cpu_write(cpu_tlbstate.pending_tlbsync, true); preempt_enable(); > + > + /* > + * Some CPUs might still be using a local ASID for this > + * process, and require IPIs, while others are using the > + * global ASID. > + * > + * In this corner case we need to do both the broadcast > + * TLB invalidation, and send IPIs. The IPIs will help > + * stragglers transition to the broadcast ASID. > + */ > + if (READ_ONCE(mm->context.asid_transition)) > + goto also_send_ipi; > + } else { > +also_send_ipi: > + inc_mm_tlb_gen(mm); > + cpumask_or(&batch->cpumask, &batch->cpumask, mm_cpumask(mm)); > + } > + mmu_notifier_arch_invalidate_secondary_tlbs(mm, 0, -1UL); > +} > + Then in switch_mm_irqs_off(), b if (this_cpu_read(cpu_tlbstate.pending_tlbsync)) tlbsync(); Note that when switch_mm_irqs_off() is called due to context switch from context_switch(), finish_task_switch() has still not took place, so the task cannot be scheduled on other cores.