linux-kernel - Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime

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Date:	Sat, 26 Sep 2015 13:19:15 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Matt Fleming <matt@...eblueprint.co.uk>
CC:	Andy Lutomirski <luto@...capital.net>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Matt Fleming <matt.fleming@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	"Lee, Chun-Yi" <jlee@...e.com>, Borislav Petkov <bp@...e.de>,
	Leif Lindholm <leif.lindholm@...aro.org>,
	Peter Jones <pjones@...hat.com>,
	James Bottomley <JBottomley@...n.com>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Dave Young <dyoung@...hat.com>,
	stable <stable@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Andy Lutomirski <luto@...nel.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Brian Gerst <brgerst@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime

Sadly a lot of firmware is known to fail in that configuration :(  That was very much our guest choice.

I don't actually think it is all that infeasible to keep relative offsets consistent for the regions we have to map. PMD_SIZE is not a very large chunk so it could be a problem.

On September 26, 2015 1:09:17 PM PDT, Ard Biesheuvel <ard.biesheuvel@...aro.org> wrote:
>
>> On 26 sep. 2015, at 12:57, Matt Fleming <matt@...eblueprint.co.uk>
>wrote:
>> 
>>> On Sat, 26 Sep, at 12:49:26PM, H. Peter Anvin wrote:
>>> 
>>> It is still a hack unless all relative offsets are preserved.  That
>>> is actually simpler, even: no sorting necessary.
>> 
>> Unless I'm missing something, preserving relative offsets is exactly
>> what we do today, modulo PMD_SIZE gaps.
>> 
>
>I think what Peter means is preserving the relative offsets inside the
>entire 1:1 space.
>
>This is not at all what we do currently, and i don't think it is
>generally feasible on 32-bit (since the physical range may conflict
>with the virtual kernel mappings)
>
>However, on 64 bit (both arm and x86), this boils down to not calling
>setVA() in the first place, which i'm all in favor of.

-- 
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