linux-kernel - Re: [PATCH 6/6] Documentation/x86: Update EFI memory region description

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Date:	Wed, 18 Nov 2015 09:18:59 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Matt Fleming <matt@...eblueprint.co.uk>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	"H . Peter Anvin" <hpa@...or.com>, Toshi Kani <toshi.kani@...com>,
	linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
	Borislav Petkov <bp@...en8.de>,
	Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Dave Jones <davej@...emonkey.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Stephen Smalley <sds@...ho.nsa.gov>
Subject: Re: [PATCH 6/6] Documentation/x86: Update EFI memory region
 description


* Matt Fleming <matt@...eblueprint.co.uk> wrote:

> On Fri, 13 Nov, at 10:22:10AM, Ingo Molnar wrote:
> > 
> > * Matt Fleming <matt@...eblueprint.co.uk> wrote:
> > 
> > > +We map EFI runtime services in the efi_pgd PGD in the virtual range of
> > > +64Gb (arbitrarily set, can be raised if needed). The mappings are not
> > > +part of any other kernel PGD and are only available during EFI runtime
> > > +calls.
> > 
> > Is that virtual address range 0-64Gb, i.e.:
> > 
> > 	0x00000000.00000000 - 0x00000010.00000000
> > 
> > or is it somewhere else?
> 
> You've snipped the patch hunk that gives the address range used,
> 
> diff --git a/Documentation/x86/x86_64/mm.txt
> b/Documentation/x86/x86_64/mm.txt
> index 05712ac83e38..a9885bb1ac22 100644
> --- a/Documentation/x86/x86_64/mm.txt
> +++ b/Documentation/x86/x86_64/mm.txt
> @@ -16,6 +16,8 @@ ffffec0000000000 - fffffc0000000000 (=44 bits) kasan
> shadow memory (16TB)
>  ... unused hole ...
>  ffffff0000000000 - ffffff7fffffffff (=39 bits) %esp fixup stacks
>  ... unused hole ...
> +ffffffef00000000 - ffffffff00000000 (=64 GB) EFI region mapping space
> +... unused hole ...
>  ffffffff80000000 - ffffffffa0000000 (=512 MB)  kernel text mapping,
> from phys 0
>  ffffffffa0000000 - ffffffffff5fffff (=1525 MB) module mapping space
>  ffffffffff600000 - ffffffffffdfffff (=8 MB) vsyscalls

Ah yes - but then the text is misleading, what does 'in the virtual range of 64Gb' 
mean? A virtual memory range is a specific range of addresses - like in the table 
you extended.

A better phrasing would be something like:

 We map EFI runtime services in the 'efi_pgd' PGD in a 64Gb large virtual memory
 window (this size is arbitrary, it can be raised later if needed).

Agreed?

Thanks,

	Ingo
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