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RE: [PATCH v2] x86, pmem: fix broken __copy_user_nocache cache-bypass assumptions

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> > Thanks for the update.  I think the alignment check should be based on
> > the following note in copy_user_nocache.
> >
> >  * Note: Cached memory copy is used when destination or size is not
> >  * naturally aligned. That is:
> >  *  - Require 8-byte alignment when size is 8 bytes or larger.
> >  *  - Require 4-byte alignment when size is 4 bytes.
> >
> > So, I think the code may be something like this.  I also made the following
> changes:
> 
> Thanks!
> 
> >  - Mask with 7, not 8.
> 
> Yes, good catch.
> 
> >  - ALIGN with cacheline size, instead of 8.
> >  - Add (bytes > flushed) test since calculation with unsigned long still results
> in a negative
> >    value (as a positive value).
> >
> >         if (bytes < 8) {
> >                 if ((dest & 3) || (bytes != 4))
> >                         arch_wb_cache_pmem(addr, 1);
> >         } else {
> >                 if (dest & 7) {
> >                         dest = ALIGN(dest, boot_cpu_data.x86_clflush_size);
> 
> Why align the destination to the next cacheline? As far as I can see
> the ALIGN_DESTINATION macro in arch/x86/include/asm/asm.h only aligns
> to the next 8-byte boundary.

The clflush here flushes for the cacheline size.  So, we do not need to flush
the same cacheline again when the unaligned tail is in the same line.

Thanks,
-Toshi

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RE: [PATCH v2] x86, pmem: fix broken __copy_user_nocache cache-bypass  assumptions "Kani, Toshimitsu" <toshi.kani@hpe.com> - 2017-04-10 21:00 +0200
  Re: [PATCH v2] x86, pmem: fix broken __copy_user_nocache cache-bypass assumptions Dan Williams <dan.j.williams@intel.com> - 2017-04-10 23:20 +0200
    RE: [PATCH v2] x86, pmem: fix broken __copy_user_nocache cache-bypass  assumptions "Kani, Toshimitsu" <toshi.kani@hpe.com> - 2017-04-10 23:30 +0200
      Re: [PATCH v2] x86, pmem: fix broken __copy_user_nocache cache-bypass assumptions Dan Williams <dan.j.williams@intel.com> - 2017-04-10 23:40 +0200
        RE: [PATCH v2] x86, pmem: fix broken __copy_user_nocache cache-bypass  assumptions "Kani, Toshimitsu" <toshi.kani@hpe.com> - 2017-04-10 23:50 +0200
          Re: [PATCH v2] x86, pmem: fix broken __copy_user_nocache cache-bypass assumptions Dan Williams <dan.j.williams@intel.com> - 2017-04-11 00:20 +0200
            RE: [PATCH v2] x86, pmem: fix broken __copy_user_nocache cache-bypass  assumptions "Kani, Toshimitsu" <toshi.kani@hpe.com> - 2017-04-11 00:50 +0200

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