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

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Date:	Wed, 30 Sep 2015 10:33:39 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Matt Fleming <matt@...eblueprint.co.uk>,
	Ingo Molnar <mingo@...nel.org>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	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>,
	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 Tue, Sep 29, 2015 at 05:56:07PM -0700, H. Peter Anvin wrote:
> On 09/29/2015 07:36 AM, Matt Fleming wrote:
> >  
> > That's a pretty good summary for x86. I think specifically the reason
> > we map the EFI memmap entries "backwards" (entry N has higher VA than
> > entry N+1) is because the code was easier to write that way, but
> > you'll know better than me ;-)
> > 
> 
> There were two reasons:
> 
> 1. The code was easier to write.
> 2. Windows did it that way.
> 
> Windows apparently broke and was changed due to this feature, too.

So can we do the 1:1 thing again?

I mean, we do create a special pagetable for EFI anyway, we can put in
there whatever we want.

I know, some apple boxes reportedly fail when 1:1 mapping is in use but
we can do the VA mapping as a workaround for them. I.e., have the 1:1
mapping be the default.

Apparently, there's not a single OS or tool which is used by fw writers
to test their brain dumplings. Windoze breakage case-in-point.

Because if there were, we'd simply do what that OS/tool does and be done
with it.

What really makes me climb the walls is when half-cooked, untested fw
hits the wild and we have to support it indefinitely.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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