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X-CSE-ConnectionGUID: QBxszIFsTOyZ6tHlrHEFNw== X-CSE-MsgGUID: tRj00Dc9TOmNlsi3e81vTw== X-IronPort-AV: E=McAfee;i="6800,10657,11807"; a="92818144" X-IronPort-AV: E=Sophos;i="6.24,187,1774335600"; d="scan'208";a="92818144" Received: from orviesa002.jf.intel.com ([10.64.159.142]) by fmvoesa104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Jun 2026 14:15:16 -0700 X-CSE-ConnectionGUID: RyvNaebvTRaJAowDbJhgMQ== X-CSE-MsgGUID: fF48+5ajQ6mu0lPmrGZtZQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.24,187,1774335600"; d="scan'208";a="274908624" Received: from ray2.jf.intel.com (HELO [10.24.81.183]) ([10.24.81.183]) by orviesa002-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Jun 2026 14:15:16 -0700 Message-ID: <60106147-5f4c-44c1-b972-e51099917bdb@intel.com> Date: Thu, 4 Jun 2026 14:15:07 -0700 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 v6 11/12] x86/mm: Enable preemption during native_flush_tlb_multi To: Chuyi Zhou , tglx@kernel.org, mingo@redhat.com, luto@kernel.org, peterz@infradead.org, paulmck@kernel.org, muchun.song@linux.dev, bp@alien8.de, dave.hansen@linux.intel.com, pbonzini@redhat.com, bigeasy@linutronix.de, clrkwllms@kernel.org, rostedt@goodmis.org, nadav.amit@gmail.com Cc: linux-kernel@vger.kernel.org References: <20260528151338.617843-1-zhouchuyi@bytedance.com> <20260528151338.617843-12-zhouchuyi@bytedance.com> Content-Language: en-US From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit First, the subject needs some improvement. Add parenthesis to functions(), please. Second, it's literally wrong: "Enable preemption during native_flush_tlb_multi". It does not do that or it at least describes it badly. It enables preemption during *one* call to native_flush_tlb_multi(). > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > index 29226d112029..d540f54f4d16 100644 > --- a/arch/x86/kernel/kvm.c > +++ b/arch/x86/kernel/kvm.c > @@ -662,8 +662,10 @@ static void kvm_flush_tlb_multi(const struct cpumask *cpumask, > u8 state; > int cpu; > struct kvm_steal_time *src; > - struct cpumask *flushmask = this_cpu_cpumask_var_ptr(__pv_cpu_mask); > + struct cpumask *flushmask; > > + guard(preempt)(); > + flushmask = this_cpu_cpumask_var_ptr(__pv_cpu_mask); > cpumask_copy(flushmask, cpumask); > /* > * We have to call flush only on online vCPUs. And This KVM modification is a complete non sequitur. It comes from nowhere. No comments. No mention in the changelog. Now, looking at how it's called, I guess flush_tlb_multi() lands here because of pv_ops. But, please have mercy on the poor reviewers and walk them through this. This could also be done in a separate patch. It's OK to disable preemption twice. > diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c > index cfc3a72477f5..58c6f3d2f993 100644 > --- a/arch/x86/mm/tlb.c > +++ b/arch/x86/mm/tlb.c > @@ -1421,9 +1421,11 @@ void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start, > if (mm_global_asid(mm)) { > broadcast_tlb_flush(info); > } else if (cpumask_any_but(mm_cpumask(mm), cpu) < nr_cpu_ids) { > + put_cpu(); > info->trim_cpumask = should_trim_cpumask(mm); > flush_tlb_multi(mm_cpumask(mm), info); > consider_global_asid(mm); > + goto invalidate; > } else if (mm == this_cpu_read(cpu_tlbstate.loaded_mm)) { > lockdep_assert_irqs_enabled(); > local_irq_disable(); > @@ -1432,6 +1434,7 @@ void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start, > } > > put_cpu(); > +invalidate: > mmu_notifier_arch_invalidate_secondary_tlbs(mm, start, end); > } I really don't like the goto. Can this be refactored to not use a goto? I'd honestly rather it be: if (foo) { broadcast_tlb_flush(info); put_cpu(); } else if (bar) { put_cpu(); flush_tlb_multi(); } else { flush_tlb_func(info); put_cpu(); } than have the goto. At least that ^ makes it obvious that each case needs a put_cpu(). But I also just generally don't like how the code is structured at this point. Does anybody have any smart ideas? > @@ -1691,7 +1694,9 @@ void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch) > invlpgb_flush_all_nonglobals(); > batch->unmapped_pages = false; > } else if (cpumask_any_but(&batch->cpumask, cpu) < nr_cpu_ids) { > + put_cpu(); > flush_tlb_multi(&batch->cpumask, &info); > + goto clear; > } else if (cpumask_test_cpu(cpu, &batch->cpumask)) { > lockdep_assert_irqs_enabled(); > local_irq_disable(); > @@ -1699,9 +1704,9 @@ void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch) > local_irq_enable(); > } > > - cpumask_clear(&batch->cpumask); > - > put_cpu(); > +clear: > + cpumask_clear(&batch->cpumask); > } I have the same general complaint about this one. This is really just hacked into place, leaving a mess for everyone in the future. It needs some careful refactoring.