linux-kernel - Re: [RFC PATCH v1 10/18] x86/efi: Access EFI related tables in the clear

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Date:	Tue, 24 May 2016 09:54:31 -0500
From:	Tom Lendacky <thomas.lendacky@....com>
To:	Borislav Petkov <bp@...en8.de>,
	Matt Fleming <matt@...eblueprint.co.uk>,
	Leif Lindholm <leif.lindholm@...aro.org>,
	Mark Salter <msalter@...hat.com>,
	Daniel Kiper <daniel.kiper@...cle.com>
CC:	<linux-arch@...r.kernel.org>, <linux-efi@...r.kernel.org>,
	<kvm@...r.kernel.org>, <linux-doc@...r.kernel.org>,
	<x86@...nel.org>, <linux-kernel@...r.kernel.org>,
	<kasan-dev@...glegroups.com>, <linux-mm@...ck.org>,
	<iommu@...ts.linux-foundation.org>,
	Radim Krčmář <rkrcmar@...hat.com>,
	Arnd Bergmann <arnd@...db.de>,
	Jonathan Corbet <corbet@....net>,
	Joerg Roedel <joro@...tes.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrey Ryabinin <aryabinin@...tuozzo.com>,
	Alexander Potapenko <glider@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [RFC PATCH v1 10/18] x86/efi: Access EFI related tables in the
 clear

On 05/12/2016 01:20 PM, Tom Lendacky wrote:
> On 05/10/2016 08:57 AM, Borislav Petkov wrote:
>> On Tue, May 10, 2016 at 02:43:58PM +0100, Matt Fleming wrote:
>>> Is it not possible to maintain some kind of kernel virtual address
>>> mapping so memremap*() and friends can figure out when to twiddle the
>>> mapping attributes and map with/without encryption?
>>
>> I guess we can move the sme_* specific stuff one indirection layer
>> below, i.e., in the *memremap() routines so that callers don't have to
>> care... That should keep the churn down...
>>
> 
> We could do that, but we'll have to generate that list of addresses so
> that it can be checked against the range being mapped.  Since this is
> part of early memmap support searching that list every time might not be
> too bad. I'll have to look into that and see what that looks like.

I looked into this and this would be a large change also to parse tables
and build lists.  It occurred to me that this could all be taken care of
if the early_memremap calls were changed to early_ioremap calls. Looking
in the git log I see that they were originally early_ioremap calls but
were changed to early_memremap calls with this commit:

commit abc93f8eb6e4 ("efi: Use early_mem*() instead of early_io*()")

Looking at the early_memremap code and the early_ioremap code they both
call __early_ioremap so I don't see how this change makes any
difference (especially since FIXMAP_PAGE_NORMAL and FIXMAP_PAGE_IO are
identical in this case).

Is it safe to change these back to early_ioremap calls (at least on
x86)?

Thanks,
Tom

> 
> Thanks,
> Tom
>