linux-kernel - Re: [PATCH -v2 0/4] EFI 1:1 mapping

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Message-ID: <51C4827B.7090208@zytor.com>
Date:	Fri, 21 Jun 2013 09:42:35 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <bp@...en8.de>
CC:	Matthew Garrett <mjg59@...f.ucam.org>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Ingo Molnar <mingo@...nel.org>,
	Linux EFI <linux-efi@...r.kernel.org>,
	Matt Fleming <matt@...sole-pimps.org>, X86 ML <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>, Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH -v2 0/4] EFI 1:1 mapping

On 06/21/2013 07:21 AM, Borislav Petkov wrote:
> On Fri, Jun 21, 2013 at 03:05:30AM -0700, H. Peter Anvin wrote:
>> If you cap it you are basically imposing a constraint on the firmware
>> and may not run properly (or at least have to turn off EFI runtime
>> calls with all that implies.)
> 
> I don't want to cap EFI just for the fun of it but rather set a limit
> so that the next one who wants a chunk of the virtual address space can
> have a reliable limit from where she/he can start. Otherwise we won't
> know where EFI reliably ends...
> 

We don't... and I don't think there is anything we can do about it.  If
some messed-up firmware wants to map a terabyte we either refuse and
don't allow EFI runtime calls on that machine or we accept it.

Fortunately the space is extremely large and with growing down from a
known address it is less likely that we'll conflict with something.

>> It might be good to have a sanity check but it needs to be pretty
>> generous.
> 
> 64 Gb generous enough?

Let's start there and see if we run into something that gives us trouble.

	-hpa


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