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Subject: Re: [PATCH 2/2] arm64/efi: Don't pad between EFI_MEMORY_RUNTIME
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To: Ingo Molnar <mingo@kernel.org>, Ard Biesheuvel <ard.biesheuvel@linaro.org>
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Cc: Matt Fleming <matt@codeblueprint.co.uk>,
        Thomas Gleixner <tglx@linutronix.de>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-efi@vger.kernel.org" <linux-efi@vger.kernel.org>,
        Leif Lindholm <leif.lindholm@linaro.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
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        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>, Borislav Petkov <bp@alien8.de>,
        Denys Vlasenko <dvlasenk@redhat.com>, Brian Gerst <brgerst@gmail.com>
From: "H. Peter Anvin" <hpa@zytor.com>
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Date: Tue, 29 Sep 2015 18:03:43 -0700
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On 09/27/2015 12:06 AM, Ingo Molnar wrote:
> 
> * Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
> 
>>> If we allocate the EFI runtime as a single virtual memory block then issues 
>>> like rounding between sections does not even come up as a problem: we map the 
>>> original offsets and sizes byte by byte.
>>
>> Well, by that reasoning, we should not call SetVirtualAddressMap() in the first 
>> place, and just use the 1:1 mapping UEFI uses natively. This is more than 
>> feasible on arm64, and I actually fought hard against using 
>> SetVirtualAddressMap() at all, but I was overruled by others. I think this is 
>> also trivially possible on X64, since the 1:1 mapping is already active 
>> alongside the VA mapping.
> 
> Could we please re-list all the arguments pro and contra of 1:1 physical mappings, 
> in a post that also explains the background so that more people can chime in, not 
> just people versed in EFI internals? It's very much possible that a bad decision 
> was made.
> 

Pro: by far the sanest way to map the UEFI tables.
Con: doesn't actually work (breaks on several known platforms.)

	-hpa