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Re: [PATCH v2] efi: Fix warning of int-to-pointer-cast on x86 32-bit builds

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On 27 October 2015 at 06:02, Matt Fleming <matt@codeblueprint.co.uk> wrote:
> On Fri, 23 Oct, at 10:37:46AM, Ard Biesheuvel wrote:
>>
>> After looking at the original (already merged) patch 11/11 again, I
>> realize this is still not right: the problem is that efi_memory_map's
>> phys_map member uses a void* type to hold a physical address, which
>> happens to be correct in the normal case even when phys_addr_t is
>> larger than void* (like on ARM with LPAE enabled) since the address it
>> holds is the address of an allocation performed by the firmware, which
>> only uses 1:1 addressable memory.
>>
>> However, overwriting memmap.phys_map with a value produced my
>> memblock_alloc() is problematic, since the allocation may be above 4
>> GB on 32-bit (L)PAE platforms. So the correct way to do this would be
>> to set the memblock limit to 4GB before memblock_alloc() on 32-bit
>> platforms, and restore it afterwards. This is a bit of a kludge,
>> though, and it would be more correct to change the type of
>> efi_memory_map::phys_map to phys_addr_t, although I don't know what
>> the potential fallout of that change is. Matt?
>
> I think that should be fine. The only potentially tricky situation we
> could encounter is where 32-bit x86 firmware uses PAE but the kernel
> is built without support.
>
> But that's not something I've ever seen enabled in the firmware and
> there's a bunch of assumptions in the kernel already that would break
> in that case.
>

Does UEFI even allow that? Even if it can describe memory over 4 GB,
it uses a flat mapping so allocations done by the stub (which
retrieves the memory map) should never reside at addresses over 4 GB.

-- 
Ard.
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[PATCH v2] efi: Fix warning of int-to-pointer-cast on x86 32-bit builds Taku Izumi <izumi.taku@jp.fujitsu.com> - 2015-10-23 02:50 +0200
  Re: [PATCH v2] efi: Fix warning of int-to-pointer-cast on x86 32-bit builds Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2015-10-23 10:40 +0200
    Re: [PATCH v2] efi: Fix warning of int-to-pointer-cast on x86 32-bit  builds Ingo Molnar <mingo@kernel.org> - 2015-10-23 11:00 +0200
      [PATCH 1/2] efi: use correct type for struct efi_memory_map::phys_map Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2015-10-23 11:50 +0200
        [PATCH 2/2] efi: Fix warning of int-to-pointer-cast on x86 32-bit builds Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2015-10-23 11:50 +0200
          Re: [PATCH 2/2] efi: Fix warning of int-to-pointer-cast on x86  32-bit builds Ingo Molnar <mingo@kernel.org> - 2015-10-23 12:30 +0200
            Re: [PATCH 2/2] efi: Fix warning of int-to-pointer-cast on x86  32-bit builds Ingo Molnar <mingo@kernel.org> - 2015-10-23 12:40 +0200
              Re: [PATCH 2/2] efi: Fix warning of int-to-pointer-cast on x86  32-bit builds Ingo Molnar <mingo@kernel.org> - 2015-10-23 12:40 +0200
                Re: [PATCH 2/2] efi: Fix warning of int-to-pointer-cast on x86  32-bit builds Matt Fleming <matt@codeblueprint.co.uk> - 2015-10-27 22:20 +0100
                Re: [PATCH 2/2] efi: Fix warning of int-to-pointer-cast on x86  32-bit builds Ingo Molnar <mingo@kernel.org> - 2015-10-28 12:40 +0100
          Re: [PATCH 2/2] efi: Fix warning of int-to-pointer-cast on x86  32-bit builds Matt Fleming <matt@codeblueprint.co.uk> - 2015-10-27 22:20 +0100
          [tip:core/efi] efi:   Fix warning of int-to-pointer-cast on x86 32-bit builds tip-bot for Taku Izumi <tipbot@zytor.com> - 2015-10-28 22:00 +0100
        Re: [PATCH 1/2] efi: use correct type for struct  efi_memory_map::phys_map Matt Fleming <matt@codeblueprint.co.uk> - 2015-10-27 22:10 +0100
        [tip:core/efi] efi: Use correct type for struct efi_memory_map::  phys_map tip-bot for Ard Biesheuvel <tipbot@zytor.com> - 2015-10-28 22:00 +0100
    Re: [PATCH v2] efi: Fix warning of int-to-pointer-cast on x86 32-bit  builds Matt Fleming <matt@codeblueprint.co.uk> - 2015-10-26 22:10 +0100
      Re: [PATCH v2] efi: Fix warning of int-to-pointer-cast on x86 32-bit builds Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2015-10-27 03:40 +0100
        Re: [PATCH v2] efi: Fix warning of int-to-pointer-cast on x86 32-bit  builds Matt Fleming <matt@codeblueprint.co.uk> - 2015-10-27 22:10 +0100
  Re: [PATCH v2] efi: Fix warning of int-to-pointer-cast on x86 32-bit  builds Ingo Molnar <mingo@kernel.org> - 2015-10-23 10:50 +0200

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