linux-kernel - Re: [PATCH v3 06/11] x86/mm: Rework lazy TLB mode and TLB freshness tracking

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Date:   Fri, 23 Jun 2017 08:22:54 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:     Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Borislav Petkov <bp@...en8.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Nadav Amit <nadav.amit@...il.com>,
        Rik van Riel <riel@...hat.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Banman <abanman@....com>, Mike Travis <travis@....com>,
        Dimitri Sivanich <sivanich@....com>,
        Juergen Gross <jgross@...e.com>
Subject: Re: [PATCH v3 06/11] x86/mm: Rework lazy TLB mode and TLB freshness tracking

On Fri, Jun 23, 2017 at 6:34 AM, Boris Ostrovsky
<boris.ostrovsky@...cle.com> wrote:
>
>> diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
>> index 1d7a7213a310..f5df56fb8b5c 100644
>> --- a/arch/x86/xen/mmu_pv.c
>> +++ b/arch/x86/xen/mmu_pv.c
>> @@ -1005,8 +1005,7 @@ static void xen_drop_mm_ref(struct mm_struct *mm)
>>         /* Get the "official" set of cpus referring to our pagetable. */
>>         if (!alloc_cpumask_var(&mask, GFP_ATOMIC)) {
>>                 for_each_online_cpu(cpu) {
>> -                       if (!cpumask_test_cpu(cpu, mm_cpumask(mm))
>> -                           && per_cpu(xen_current_cr3, cpu) !=
>> __pa(mm->pgd))
>> +                       if (per_cpu(xen_current_cr3, cpu) !=
>> __pa(mm->pgd))
>>                                 continue;
>>                         smp_call_function_single(cpu,
>> drop_mm_ref_this_cpu, mm, 1);
>>                 }
>>
>
>
> I wonder then whether
>         cpumask_copy(mask, mm_cpumask(mm));
> immediately below is needed.

Probably not.  I'll change it to cpumask_clear().  Then the two cases
in that function match better.

>
> -boris