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Re: [PATCH v6 14/19] arm64:ilp32: add sys_ilp32.c and a separate table (in entry.S) to use it

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On Thu, Dec 03, 2015 at 05:47:08PM +0000, Catalin Marinas wrote:
> On Wed, Dec 02, 2015 at 12:29:04AM +0300, Yury Norov wrote:
> > My question. Why aarch64 defines COMPAT_SHMLBA as 0x4000?
> 
> This was done to match the arch/arm value of 4 * 4K. The historical
> 32-bit reason for 4 pages is to cope with aliasing VIPT caches (see
> https://git.kernel.org/cgit/linux/kernel/git/tglx/history.git/commit?id=4197692eef113eeb8e3e413cc70993a5e667e5b8)
> 
> > If there's
> > no specific reason for it, it looks like a bug, and we should
> > define it like in arch/arm:
> >         #define SHMLBA  (4 * PAGE_SIZE)          /* attach addr a multiple of this */
> 
> I guess you meant COMPAT_SHMLBA.

I citated arm code here. In aarch64 it's COMPAT_SHMLBA, of course.

> I'm not sure there is much value in
> keeping 4*PAGE_SIZE for larger page sizes but I agree that the current
> 16K value doesn't work well with 64K pages.

Arnd told there will be a workaround for arm v6 caches. Than this
header will not be needed at all. Until that, this is simpliest
fix as it doesn't affect userspace.

> 
> -- 
> Catalin
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Re: [PATCH v6 14/19] arm64:ilp32: add sys_ilp32.c and a separate  table (in entry.S) to use it Yury Norov <ynorov@caviumnetworks.com> - 2015-12-01 22:40 +0100
  Re: [PATCH v6 14/19] arm64:ilp32: add sys_ilp32.c and a separate table (in entry.S) to use it Arnd Bergmann <arnd@arndb.de> - 2015-12-01 23:50 +0100
    Re: [PATCH v6 14/19] arm64:ilp32: add sys_ilp32.c and a separate  table (in entry.S) to use it Yury Norov <ynorov@caviumnetworks.com> - 2015-12-02 00:40 +0100
      Re: [PATCH v6 14/19] arm64:ilp32: add sys_ilp32.c and a separate table (in entry.S) to use it Arnd Bergmann <arnd@arndb.de> - 2015-12-02 09:40 +0100
        Re: [PATCH v6 14/19] arm64:ilp32: add sys_ilp32.c and a separate  table (in entry.S) to use it Yury Norov <ynorov@caviumnetworks.com> - 2015-12-02 10:20 +0100
        Re: [PATCH v6 14/19] arm64:ilp32: add sys_ilp32.c and a separate  table (in entry.S) to use it Yury Norov <ynorov@caviumnetworks.com> - 2015-12-02 11:40 +0100
          Re: [PATCH v6 14/19] arm64:ilp32: add sys_ilp32.c and a separate table (in entry.S) to use it Arnd Bergmann <arnd@arndb.de> - 2015-12-02 14:50 +0100
            Re: [PATCH v6 14/19] arm64:ilp32: add sys_ilp32.c and a separate table (in entry.S) to use it Arnd Bergmann <arnd@arndb.de> - 2015-12-02 15:00 +0100
              Re: [PATCH v6 14/19] arm64:ilp32: add sys_ilp32.c and a separate  table (in entry.S) to use it Will Deacon <will.deacon@arm.com> - 2015-12-02 15:00 +0100
  Re: [PATCH v6 14/19] arm64:ilp32: add sys_ilp32.c and a separate  table (in entry.S) to use it Catalin Marinas <catalin.marinas@arm.com> - 2015-12-03 18:50 +0100
    Re: [PATCH v6 14/19] arm64:ilp32: add sys_ilp32.c and a separate  table (in entry.S) to use it Yury Norov <ynorov@caviumnetworks.com> - 2015-12-03 19:20 +0100
      Re: [PATCH v6 14/19] arm64:ilp32: add sys_ilp32.c and a separate table (in entry.S) to use it Arnd Bergmann <arnd@arndb.de> - 2015-12-03 21:50 +0100

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