linux-kernel - Re: [edk2] Corrupted EFI region

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Date:	Tue, 06 Aug 2013 09:26:57 +0200
From:	Laszlo Ersek <lersek@...hat.com>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
CC:	Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>,
	Andrew Fish <afish@...le.com>,
	edk2-devel@...ts.sourceforge.net, linux-efi@...r.kernel.org,
	Gleb Natapov <gleb@...hat.com>,
	lkml <linux-kernel@...r.kernel.org>,
	David Woodhouse <dwmw2@...radead.org>
Subject: Re: [edk2] Corrupted EFI region

On 08/06/13 00:52, James Bottomley wrote:
> On Mon, 2013-08-05 at 23:55 +0200, Laszlo Ersek wrote:
>> On 08/05/13 23:41, Borislav Petkov wrote:
>>> On Mon, Aug 05, 2013 at 02:37:08PM -0700, H. Peter Anvin wrote:
>>>> All of this would be a non-problem if there weren't buggy
>>>> implementations which can't run *without* SetVirtualAddressMap().
>>>
>>> Oh, you mean, if we were to call the runtime services through their
>>> physical addresses?
>>
>> I heard that there was a (U)EFI firmware implementation that didn't even
>> implement SetVirtualAddressMap(). It was okay because the main OS for
>> that platform didn't want to call it, it thunked to physical mode for
>> each runtime service call.
>>
>> (This is not hearsay; I'm omitting the specifics because I'm not sure if
>> I'm allowed to give any. I've heard about this stuff from a direct
>> colleague who used to work on these systems.)
> 
> That's actually the way all non-x86 unix systems operate.  If you look
> in the firmware mechanisms for almost every non-x86 system in the Linux
> kernel architecture directories they do this if they have to access
> firmware from Linux (we do it a lot on parisc to get the IODC to give us
> the device inventory for instance).
> 
> I strongly suspect the origin of this weirdness is that once upon a time
> windows didn't run with a separated address space and so needed a way of
> accessing firmware in the same address space, hence the pointer
> relocation trick, but even windows hasn't needed this for a while.

Thank you for educating me.
Laszlo

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