linux-kernel - Re: [PATCH 2/2] arm64/efi: Don't pad between EFI_MEMORY

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Message-ID: <560B34EF.8040408@zytor.com>
Date:	Tue, 29 Sep 2015 18:03:43 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...nel.org>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:	Matt Fleming <matt@...eblueprint.co.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	Leif Lindholm <leif.lindholm@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>,
	Matt Fleming <matt.fleming@...el.com>,
	Mark Rutland <mark.rutland@....com>,
	Mark Salter <msalter@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Brian Gerst <brgerst@...il.com>
Subject: Re: [PATCH 2/2] arm64/efi: Don't pad between EFI_MEMORY_RUNTIME
 regions

On 09/27/2015 12:06 AM, Ingo Molnar wrote:
> 
> * Ard Biesheuvel <ard.biesheuvel@...aro.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


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