linux-kernel - Re: [PATCH] Fix left over EFI cache mapping problems

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Date:	Thu, 14 Feb 2008 19:38:19 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	torvalds@...l.org, tglx@...utronix.de,
	linux-kernel@...r.kernel.org, ying.huang@...el.com
Subject: Re: [PATCH] Fix left over EFI cache mapping problems

* Andi Kleen <andi@...stfloor.org> wrote:

> > this is indeed a bug (we change the attributes for a larger area 
> > than needed), but your fix is unclean. Find below a cleaner 
> > solution.
> 
> You're still ignoring the other problem of set_memory_uc() not 
> handling fixmap and ioremap correctly. [...]

No, we did not ignore it, and yes, you are wrong.

One thing that you miss is that the 64-bit EFI runtime has to be marked 
uncacheable only if it the EFI image attribute signals an uncacheable 
area:

                if (!(md->attribute & EFI_MEMORY_WB))
                        set_memory_uc(md->virt_addr, md->num_pages);

and Linux EFI does not support device EFI runtimes. So your observation, 
while correct for non-RAM 64-bit EFI images, is theoretical at the 
moment and has no practical relevance.

Of course, as we've stated it numerous times, we want this all fixed up, 
and we _have_ fixed it up already, but we wanted to do it properly. 
Right now we've got the fixes lined up and we are waiting for a test 
report and an Ack from Ying Huang. (he reported that current -git worked 
just fine for him)

Also note that 64-bit EFI runtime support (the ability to execute EFI 
code) is completely new - it got introduced 14 days ago. We only use 
fixmaps on 64-bit EFI.

32-bit EFI is more common (but still not very common, compared to other 
x86 platforms) and that is totally unaffected by secondary aliases. 
(which is a complication of the 64-bit kernel)

Thanks,

	Ingo
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