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Re: [BUG] random kernel crashes after THP rework on s390 (maybe also on PowerPC and ARM)

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On Wed, Feb 24, 2016 at 11:51:47AM +0100, Christian Borntraeger wrote:
> On 02/24/2016 11:41 AM, Will Deacon wrote:
> > On Wed, Feb 24, 2016 at 11:16:34AM +0100, Christian Borntraeger wrote:
> >> Without that fix we would clearly have stale tlb entries, no?
> > 
> > Yes, but AFAIU the sequence on arm64 is:
> > 
> > 1.  trans huge mapping (block mapping in arm64 speak)
> > 2.  faulting entry (pmd_mknotpresent)
> > 3.  tlb invalidation
> > 4.  table entry mapping the same pages as (1).
> > 
> > so if the microarchitecture we're on can tolerate a mixture of block
> > mappings and page mappings mapping the same VA to the same PA, then the
> > lack of TLB maintenance would go unnoticed. There are certainly systems
> > where that could cause an issue, but I believe the one I've been testing
> > on would be ok.
> 
> So in essence you say it does not matter that you flush the wrong range in 
> flush_pmd_tlb_range as long as it will be flushed later on when the pages
> really go away. Yes, then it really might be ok for arm64.

Indeed, although that's a property of the microarchitecture I'm using
rather than an architectural guarantee so the code should certainly be
fixed!

Will

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Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) "Kirill A. Shutemov" <kirill@shutemov.name> - 2016-02-23 13:20 +0100
  Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) Linus Torvalds <torvalds@linux-foundation.org> - 2016-02-23 18:50 +0100
  Re: [BUG] random kernel crashes after THP rework on s390 (maybe  also on PowerPC and ARM) Gerald Schaefer <gerald.schaefer@de.ibm.com> - 2016-02-23 19:20 +0100
    Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) Will Deacon <will.deacon@arm.com> - 2016-02-23 19:50 +0100
      Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) Steve Capper <steve.capper@linaro.org> - 2016-02-25 16:50 +0100
        Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) "Kirill A. Shutemov" <kirill@shutemov.name> - 2016-02-25 17:10 +0100
          Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) Steve Capper <steve.capper@linaro.org> - 2016-02-25 17:10 +0100
    Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) Will Deacon <will.deacon@arm.com> - 2016-02-23 21:30 +0100
      Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) Christian Borntraeger <borntraeger@de.ibm.com> - 2016-02-24 11:20 +0100
        Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) Will Deacon <will.deacon@arm.com> - 2016-02-24 11:50 +0100
          Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) Christian Borntraeger <borntraeger@de.ibm.com> - 2016-02-24 12:00 +0100
            Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) Will Deacon <will.deacon@arm.com> - 2016-02-24 12:10 +0100
            Re: [BUG] random kernel crashes after THP rework on s390 (maybe also on PowerPC and ARM) "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> - 2016-02-24 18:30 +0100
    Re: [BUG] random kernel crashes after THP rework on s390 (maybe  also on PowerPC and ARM) Martin Schwidefsky <schwidefsky@de.ibm.com> - 2016-02-24 09:30 +0100
    Re: [BUG] random kernel crashes after THP rework on s390 (maybe  also on PowerPC and ARM) Martin Schwidefsky <schwidefsky@de.ibm.com> - 2016-02-24 09:40 +0100
      Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) Sebastian Ott <sebott@linux.vnet.ibm.com> - 2016-02-24 13:20 +0100
    Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) "Kirill A. Shutemov" <kirill@shutemov.name> - 2016-02-24 10:20 +0100
      Re: [BUG] random kernel crashes after THP rework on s390 (maybe  also on PowerPC and ARM) Gerald Schaefer <gerald.schaefer@de.ibm.com> - 2016-02-24 17:50 +0100

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