Re: [HELP-NEEDED, PATCH 0/3] Do not loose dirty bit on THP pages

From	Vlastimil Babka <vbabka@suse.cz>
Newsgroups	linux.kernel
Subject	Re: [HELP-NEEDED, PATCH 0/3] Do not loose dirty bit on THP pages
Date	2017-06-14 19:10 +0200
Message-ID	<tSjXP-7Wy-9@gated-at.bofh.it> (permalink)
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On 06/14/2017 06:55 PM, Will Deacon wrote:
>>
>> May be we should relook at pmd PTE udpate interface. We really need an
>> interface that can update pmd entries such that we don't clear it in
>> between. IMHO, we can avoid the pmdp_invalidate() completely, if we can
>> switch from a pmd PTE entry to a pointer to PTE page (pgtable_t). We also
>> need this interface to avoid the madvise race fixed by
> 
> There's a good chance I'm not following your suggestion here, but it's
> probably worth me pointing out that swizzling a page table entry from a
> block mapping (e.g. a huge page mapped at the PMD level) to a table entry
> (e.g. a pointer to a page of PTEs) can lead to all sorts of horrible
> problems on ARM, including amalgamation of TLB entries and fatal aborts.

AFAIK some AMD x86_64 CPU's had the same problem and generated MCE's,
and on Intel there are some restrictions when you can do that. See the
large comment in __split_huge_pmd_locked().

> So we really need to go via an invalid entry, with appropriate TLB
> invalidation before installing the new entry.
> 
> Will
>

Thread

[HELP-NEEDED, PATCH 0/3] Do not loose dirty bit on THP pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-06-14 16:00 +0200
  [PATCH 2/3] mm: Do not loose dirty and access bits in pmdp_invalidate() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-06-14 16:00 +0200
  Re: [HELP-NEEDED, PATCH 0/3] Do not loose dirty bit on THP pages Martin Schwidefsky <schwidefsky@de.ibm.com> - 2017-06-14 16:10 +0200
  Re: [HELP-NEEDED, PATCH 0/3] Do not loose dirty bit on THP pages "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> - 2017-06-14 17:30 +0200
    Re: [HELP-NEEDED, PATCH 0/3] Do not loose dirty bit on THP pages Will Deacon <will.deacon@arm.com> - 2017-06-14 19:00 +0200
      Re: [HELP-NEEDED, PATCH 0/3] Do not loose dirty bit on THP pages Vlastimil Babka <vbabka@suse.cz> - 2017-06-14 19:10 +0200
        Re: [HELP-NEEDED, PATCH 0/3] Do not loose dirty bit on THP pages "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> - 2017-06-15 03:40 +0200
      Re: [HELP-NEEDED, PATCH 0/3] Do not loose dirty bit on THP pages "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> - 2017-06-15 03:10 +0200
        Re: [HELP-NEEDED, PATCH 0/3] Do not loose dirty bit on THP pages "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> - 2017-06-15 05:00 +0200
        Re: [HELP-NEEDED, PATCH 0/3] Do not loose dirty bit on THP pages "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-06-15 10:50 +0200
          Re: [HELP-NEEDED, PATCH 0/3] Do not loose dirty bit on THP pages "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> - 2017-06-15 11:40 +0200

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