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Subject: Re: [RFC 03/10] x86/mm: Make the batched unmap TLB flush API more
 generic
To: Andy Lutomirski <luto@kernel.org>, X86 ML <x86@kernel.org>
References: <cover.1494160201.git.luto@kernel.org>
 <983c5ee661d8fe8a70c596c4e77076d11ce3f80a.1494160201.git.luto@kernel.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Borislav Petkov <bpetkov@suse.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mel Gorman <mgorman@suse.de>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        Rik van Riel <riel@redhat.com>, Nadav Amit <namit@vmware.com>,
        Michal Hocko <mhocko@suse.com>, Sasha Levin <sasha.levin@oracle.com>
From: Dave Hansen <dave.hansen@intel.com>
Message-ID: <d36207ef-a4b3-24ef-40e4-9e6a22b092cb@intel.com>
Date: Mon, 8 May 2017 08:34:58 -0700
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On 05/07/2017 05:38 AM, Andy Lutomirski wrote:
> diff --git a/mm/rmap.c b/mm/rmap.c
> index f6838015810f..2e568c82f477 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -579,25 +579,12 @@ void page_unlock_anon_vma_read(struct anon_vma *anon_vma)
>  void try_to_unmap_flush(void)
>  {
>  	struct tlbflush_unmap_batch *tlb_ubc = &current->tlb_ubc;
> -	int cpu;
>  
>  	if (!tlb_ubc->flush_required)
>  		return;
>  
> -	cpu = get_cpu();
> -
> -	if (cpumask_test_cpu(cpu, &tlb_ubc->cpumask)) {
> -		count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ALL);
> -		local_flush_tlb();
> -		trace_tlb_flush(TLB_LOCAL_SHOOTDOWN, TLB_FLUSH_ALL);
> -	}
> -
> -	if (cpumask_any_but(&tlb_ubc->cpumask, cpu) < nr_cpu_ids)
> -		flush_tlb_others(&tlb_ubc->cpumask, NULL, 0, TLB_FLUSH_ALL);
> -	cpumask_clear(&tlb_ubc->cpumask);
>  	tlb_ubc->flush_required = false;
>  	tlb_ubc->writable = false;
> -	put_cpu();
>  }
>  
>  /* Flush iff there are potentially writable TLB entries that can race with IO */
> @@ -613,7 +600,7 @@ static void set_tlb_ubc_flush_pending(struct mm_struct *mm, bool writable)
>  {
>  	struct tlbflush_unmap_batch *tlb_ubc = &current->tlb_ubc;
>  
> -	cpumask_or(&tlb_ubc->cpumask, &tlb_ubc->cpumask, mm_cpumask(mm));
> +	arch_tlbbatch_add_mm(&tlb_ubc->arch, mm);
>  	tlb_ubc->flush_required = true;
>  
>  	/*

Looking at this patch in isolation, how can this be safe?  It removes
TLB flushes from the generic code.  Do other patches in the series fix
this up?