linux-kernel - Re: [PATCH v5 4/8] x86/mm/tlb: Flush remote and local TLBs concurrently

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Date:   Tue, 16 Feb 2021 19:17:54 +0000
From:   Nadav Amit <namit@...are.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Sasha Levin <sashal@...nel.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        X86 ML <x86@...nel.org>, Juergen Gross <jgross@...e.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        Linux Virtualization <virtualization@...ts.linux-foundation.org>,
        KVM <kvm@...r.kernel.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        Michael Kelley <mikelley@...rosoft.com>
Subject: Re: [PATCH v5 4/8] x86/mm/tlb: Flush remote and local TLBs
 concurrently

> On Feb 16, 2021, at 4:10 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> 
> On Tue, Feb 09, 2021 at 02:16:49PM -0800, Nadav Amit wrote:
>> @@ -816,8 +821,8 @@ STATIC_NOPV void native_flush_tlb_others(const struct cpumask *cpumask,
>> 	 * doing a speculative memory access.
>> 	 */
>> 	if (info->freed_tables) {
>> -		smp_call_function_many(cpumask, flush_tlb_func,
>> -			       (void *)info, 1);
>> +		on_each_cpu_cond_mask(NULL, flush_tlb_func, (void *)info, true,
>> +				      cpumask);
>> 	} else {
>> 		/*
>> 		 * Although we could have used on_each_cpu_cond_mask(),
>> @@ -844,14 +849,15 @@ STATIC_NOPV void native_flush_tlb_others(const struct cpumask *cpumask,
>> 			if (tlb_is_not_lazy(cpu))
>> 				__cpumask_set_cpu(cpu, cond_cpumask);
>> 		}
>> -		smp_call_function_many(cond_cpumask, flush_tlb_func, (void *)info, 1);
>> +		on_each_cpu_cond_mask(NULL, flush_tlb_func, (void *)info, true,
>> +				      cpumask);
>> 	}
>> }
> 
> Surely on_each_cpu_mask() is more appropriate? There the compiler can do
> the NULL propagation because it's on the same TU.
> 
> --- a/arch/x86/mm/tlb.c
> +++ b/arch/x86/mm/tlb.c
> @@ -821,8 +821,7 @@ STATIC_NOPV void native_flush_tlb_multi(
> 	 * doing a speculative memory access.
> 	 */
> 	if (info->freed_tables) {
> -		on_each_cpu_cond_mask(NULL, flush_tlb_func, (void *)info, true,
> -				      cpumask);
> +		on_each_cpu_mask(cpumask, flush_tlb_func, (void *)info, true);
> 	} else {
> 		/*
> 		 * Although we could have used on_each_cpu_cond_mask(),
> @@ -849,8 +848,7 @@ STATIC_NOPV void native_flush_tlb_multi(
> 			if (tlb_is_not_lazy(cpu))
> 				__cpumask_set_cpu(cpu, cond_cpumask);
> 		}
> -		on_each_cpu_cond_mask(NULL, flush_tlb_func, (void *)info, true,
> -				      cpumask);
> +		on_each_cpu_mask(cpumask, flush_tlb_func, (void *)info, true);
> 	}
> }

Indeed, and there is actually an additional bug - I used cpumask in the
second on_each_cpu_cond_mask() instead of cond_cpumask.