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Mon, 20 Jan 2025 01:56:32 -0800 (PST) Received: from [132.69.243.144] ([132.69.243.144]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-ab384c61311sm603137166b.18.2025.01.20.01.56.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 20 Jan 2025 01:56:31 -0800 (PST) Message-ID: <13bc0c49-09a4-434e-bd35-1ea50be38e25@gmail.com> Date: Mon, 20 Jan 2025 11:56:29 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 10/12] x86,tlb: do targeted broadcast flushing from tlbbatch code To: Rik van Riel , x86@kernel.org Cc: linux-kernel@vger.kernel.org, bp@alien8.de, peterz@infradead.org, dave.hansen@linux.intel.com, zhengqi.arch@bytedance.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 References: <20250116023127.1531583-1-riel@surriel.com> <20250116023127.1531583-11-riel@surriel.com> Content-Language: en-US From: Nadav Amit Autocrypt: addr=nadav.amit@gmail.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 16/01/2025 4:30, Rik van Riel wrote: > Instead of doing a system-wide TLB flush from arch_tlbbatch_flush, > queue up asynchronous, targeted flushes from arch_tlbbatch_add_pending. > [snip] > --- a/arch/x86/mm/tlb.c > +++ b/arch/x86/mm/tlb.c > @@ -1659,9 +1659,7 @@ void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch) > * a local TLB flush is needed. Optimize this use-case by calling > * flush_tlb_func_local() directly in this case. > */ > - if (cpu_feature_enabled(X86_FEATURE_INVLPGB)) { > - invlpgb_flush_all_nonglobals(); > - } else if (cpumask_any_but(&batch->cpumask, cpu) < nr_cpu_ids) { > + if (cpumask_any_but(&batch->cpumask, cpu) < nr_cpu_ids) { > flush_tlb_multi(&batch->cpumask, info); > } else if (cpumask_test_cpu(cpu, &batch->cpumask)) { > lockdep_assert_irqs_enabled(); > @@ -1670,12 +1668,62 @@ void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch) > local_irq_enable(); > } > > + /* > + * If we issued (asynchronous) INVLPGB flushes, wait for them here. > + * The cpumask above contains only CPUs that were running tasks > + * not using broadcast TLB flushing. > + */ > + if (cpu_feature_enabled(X86_FEATURE_INVLPGB) && batch->used_invlpgb) { > + tlbsync(); > + migrate_enable(); Maybe someone mentioned it before, but I would emphasize that I do not think that preventing migration for potentially long time is that great. One alternative solution would be to set a bit on cpu_tlbstate, that when set, you'd issue a tlbsync on context switch. (I can think about other solutions, but I think the one I just mentioned is the cleanest one). > + batch->used_invlpgb = false; > + } > + > cpumask_clear(&batch->cpumask); > > put_flush_tlb_info(); > put_cpu(); > } > > +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 (!batch->used_invlpgb) { > + batch->used_invlpgb = true; > + migrate_disable(); See my comment above... > + } > + 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); > + > + /* > + * 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: I really think you should avoid such goto's. A simple bool variable of "need_ipi" would suffice. > + inc_mm_tlb_gen(mm); > + cpumask_or(&batch->cpumask, &batch->cpumask, mm_cpumask(mm)); > + } > + mmu_notifier_arch_invalidate_secondary_tlbs(mm, 0, -1UL); > +} > + > /* > * Blindly accessing user memory from NMI context can be dangerous > * if we're in the middle of switching the current user task or