linux-kernel - Re: [PATCH] Map in physical addresses in efi_map_region

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Message-ID: <20160815150709.GA6085@nazgul.tnic>
Date:	Mon, 15 Aug 2016 17:07:09 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Matt Fleming <matt@...eblueprint.co.uk>
Cc:	Alex Thorlton <athorlton@....com>, linux-kernel@...r.kernel.org,
	Russ Anderson <rja@....com>,
	Dimitri Sivanich <sivanich@....com>,
	Mike Travis <travis@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-efi@...r.kernel.org, Dave Young <dyoung@...hat.com>
Subject: Re: [PATCH] Map in physical addresses in efi_map_region_fixed

On Mon, Aug 15, 2016 at 01:42:58PM +0100, Matt Fleming wrote:
> (Cc'ing Boris and Dave)
> 
> On Fri, 05 Aug, at 06:59:35PM, Alex Thorlton wrote:
> > This is a simple change to add in the physical mappings as well as the
> > virtual mappings in efi_map_region_fixed.  The motivation here is to
> > get access to EFI runtime code that is only available via the 1:1
> > mappings on a kexec'd kernel.

So I don't understand: the whole jumping through hoops so that we have
stable virtual mappings just so that the kexec-ed kernel can call EFI
runtime, is now useless?!

What if the physical address is occupied by the kexec kernel?

Why do you guys need the physical mapping all of a sudden?

Your patch is basically rendering all the effort moot and we could've
saved ourselves all that trouble of doing all that virtual address
mapping and done the 1:1 thing.

Which really is probably simpler since we have an EFI-specific page
table and running EFI in the kexec-ed kernel would mean basically
recreating it.

What am I missing?

commit d2f7cbe7b26a74dbbbf8f325b2a6fd01bc34032c
Author: Borislav Petkov <bp@...e.de>
Date:   Thu Oct 31 17:25:08 2013 +0100

    x86/efi: Runtime services virtual mapping
    
    We map the EFI regions needed for runtime services non-contiguously,
    with preserved alignment on virtual addresses starting from -4G down
    for a total max space of 64G. This way, we provide for stable runtime
    services addresses across kernels so that a kexec'd kernel can still use
    them.

-- 
Regards/Gruss,
    Boris.

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