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Re: [PATCHv4 08/10] mm/kasan: Switch to using __pa_symbol and lm_alias

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On Thu, Dec 01, 2016 at 02:36:05PM +0300, Andrey Ryabinin wrote:
> On 11/29/2016 09:55 PM, Laura Abbott wrote:
> > __pa_symbol is the correct API to find the physical address of symbols.
> > Switch to it to allow for debugging APIs to work correctly.
> 
> But __pa() is correct for symbols. I see how __pa_symbol() might be a little
> faster than __pa(), but there is nothing wrong in using __pa() on symbols.

While it's true today that __pa() works on symbols, this is for
pragmatic reasons (allowing existing code to work until it is all
cleaned up), and __pa_symbol() is the correct API to use.

Relying on this means that __pa() can't be optimised for the (vastly
common) case of translating linear map addresses.

Consistent use of __pa_symbol() will allow for subsequent optimisation
of __pa() in the common case, in adition to being necessary for arm64's
DEBUG_VIRTUAL.

> > Other functions such as p*d_populate may call __pa internally.
> > Ensure that the address passed is in the linear region by calling
> > lm_alias.
> 
> Why it should be linear mapping address? __pa() translates kernel
> image address just fine.

As above, while that's true today, but is something that we wish to
change. 

> Generated code is probably worse too.

Even if that is the case, given this is code run once at boot on a debug
build, I think it's outweighed by the gain from DEBUG_VIRTUAL, and as a
step towards optimising __pa().

Thanks,
Mark.

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[PATCHv4 00/10] CONFIG_DEBUG_VIRTUAL for arm64 Laura Abbott <labbott@redhat.com> - 2016-11-29 20:00 +0100
  [PATCHv4 09/10] mm/usercopy: Switch to using lm_alias Laura Abbott <labbott@redhat.com> - 2016-11-29 20:00 +0100
    Re: [PATCHv4 09/10] mm/usercopy: Switch to using lm_alias Kees Cook <keescook@chromium.org> - 2016-11-29 20:40 +0100
      Re: [PATCHv4 09/10] mm/usercopy: Switch to using lm_alias Mark Rutland <mark.rutland@arm.com> - 2016-12-06 19:20 +0100
        Re: [PATCHv4 09/10] mm/usercopy: Switch to using lm_alias Kees Cook <keescook@chromium.org> - 2016-12-06 21:20 +0100
          Re: [PATCHv4 09/10] mm/usercopy: Switch to using lm_alias Mark Rutland <mark.rutland@arm.com> - 2016-12-07 15:00 +0100
    Re: [PATCHv4 09/10] mm/usercopy: Switch to using lm_alias Mark Rutland <mark.rutland@arm.com> - 2016-12-06 19:30 +0100
  [PATCHv4 10/10] arm64: Add support for CONFIG_DEBUG_VIRTUAL Laura Abbott <labbott@redhat.com> - 2016-11-29 20:00 +0100
    Re: [PATCHv4 10/10] arm64: Add support for CONFIG_DEBUG_VIRTUAL Mark Rutland <mark.rutland@arm.com> - 2016-12-06 20:00 +0100
  [PATCHv4 08/10] mm/kasan: Switch to using __pa_symbol and lm_alias Laura Abbott <labbott@redhat.com> - 2016-11-29 20:00 +0100
    Re: [PATCHv4 08/10] mm/kasan: Switch to using __pa_symbol and  lm_alias Laura Abbott <labbott@redhat.com> - 2016-12-01 20:20 +0100
    Re: [PATCHv4 08/10] mm/kasan: Switch to using __pa_symbol and  lm_alias Mark Rutland <mark.rutland@arm.com> - 2016-12-06 18:30 +0100
    Re: [PATCHv4 08/10] mm/kasan: Switch to using __pa_symbol and  lm_alias Mark Rutland <mark.rutland@arm.com> - 2016-12-06 18:50 +0100
    Re: [PATCHv4 08/10] mm/kasan: Switch to using __pa_symbol and  lm_alias Mark Rutland <mark.rutland@arm.com> - 2016-12-06 20:30 +0100
  [PATCHv4 06/10] xen: Switch to using __pa_symbol Laura Abbott <labbott@redhat.com> - 2016-11-29 20:00 +0100
    Re: [PATCHv4 06/10] xen: Switch to using __pa_symbol Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-11-29 23:30 +0100
      Re: [PATCHv4 06/10] xen: Switch to using __pa_symbol Laura Abbott <labbott@redhat.com> - 2016-11-29 23:50 +0100
  [PATCH 0/3] ARM: Add support for CONFIG_DEBUG_VIRTUAL Florian Fainelli <f.fainelli@gmail.com> - 2016-12-06 21:00 +0100
    [PATCH 3/3] ARM: Add support for CONFIG_DEBUG_VIRTUAL Florian Fainelli <f.fainelli@gmail.com> - 2016-12-06 21:00 +0100
      Re: [PATCH 3/3] ARM: Add support for CONFIG_DEBUG_VIRTUAL Florian Fainelli <f.fainelli@gmail.com> - 2016-12-06 21:50 +0100
      Re: [PATCH 3/3] ARM: Add support for CONFIG_DEBUG_VIRTUAL Laura Abbott <labbott@redhat.com> - 2016-12-07 03:10 +0100
        Re: [PATCH 3/3] ARM: Add support for CONFIG_DEBUG_VIRTUAL Florian Fainelli <f.fainelli@gmail.com> - 2016-12-07 03:30 +0100
    [PATCH 2/3] ARM: Utilize __pa_symbol in lieu of __pa Florian Fainelli <f.fainelli@gmail.com> - 2016-12-06 21:00 +0100
    [PATCH 1/3] ARM: Define KERNEL_START and KERNEL_END Florian Fainelli <f.fainelli@gmail.com> - 2016-12-06 21:00 +0100
      Re: [PATCH 1/3] ARM: Define KERNEL_START and KERNEL_END Florian Fainelli <f.fainelli@gmail.com> - 2016-12-06 23:50 +0100
      RE: [PATCH 1/3] ARM: Define KERNEL_START and KERNEL_END Chris Brandt <Chris.Brandt@renesas.com> - 2016-12-06 23:50 +0100
      Re: [PATCH 1/3] ARM: Define KERNEL_START and KERNEL_END kbuild test robot <lkp@intel.com> - 2016-12-07 07:20 +0100

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