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Date:	Thu, 03 Jan 2013 15:50:55 +0000
From:	Matt Fleming <matt.fleming@...el.com>
To:	Robin Holt <holt@....com>
Cc:	Nathan Zimmer <nzimmer@....com>, "H. Peter Anvin" <hpa@...or.com>,
	linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
	tglx@...utronix.de, mingo@...hat.com
Subject: Re: BUG: unable to handle kernel paging request at 000000effd870020

On Wed, 2013-01-02 at 15:09 -0600, Robin Holt wrote:
> On Wed, Jan 02, 2013 at 01:13:43PM -0600, Nathan Zimmer wrote:
> > On 01/02/2013 12:04 PM, H. Peter Anvin wrote:
> > >On 01/02/2013 09:21 AM, Nathan Zimmer wrote:
> > >>I am getting an early boot problem. It only happens on the larger of the
> > >>machines I haven't seen it crop up on machines with more then 512 GB of ram.
> > >>It shows in the latest linus kernel too.
> > >>
> > >>I am (wildly) guessing that what is happening is that the new_memmap that is
> > >>being passed to bios is somehow placed incorrectly.
> > >>I have come up with a workaround.  By placing it the DMA area the issue goes
> > >>away but that doesn't seem like a real fix.
> > >>
> > >What does your memory map look like?
> 
> We reported this a few times (Russ Anderson and I both).  The problem is
> at the point in boot where the efi_enter_virtual_mode callback is, there
> is no identity mapping for most of memory.  If the allocation happens
> to be above the 512GB (or maybe something lower than that) point, the
> BIOS is not able to address this via the physical address passed to it.

Right, looks like efi_call_phys_prelog() needs rewriting to install a
proper identity mapping that actually addresses *all* of available
memory, instead of just the first PGDIR_SIZE bytes.


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