linux-kernel - Re: [RFC v2 0/2] Early use of boot service memory

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Date:	Fri, 22 Nov 2013 01:16:13 +0000
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	jerry.hoemann@...com
Cc:	rob@...dley.net, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, x86@...nel.org, matt.fleming@...el.com,
	yinghai@...nel.org, akpm@...ux-foundation.org, bp@...e.de,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-efi@...r.kernel.org, penberg@...nel.org,
	mingo.kernel.org@...il.com, vgoyal@...hat.com
Subject: Re: [RFC v2 0/2] Early use of boot service memory

On Thu, Nov 21, 2013 at 06:05:15PM -0700, jerry.hoemann@...com wrote:
> On Thu, Nov 21, 2013 at 11:38:31PM +0000, Matthew Garrett wrote:
> > Hm. If the problem is fragmentation, then yeah, I can imagine this 
> > causing problems. In that case we could take a two-pass approach - find 
> > a gap that *will* be big enough, reserve everything that isn't currently 
> > reserved, and then reserve the rest after ExitBootServices()?
> 
> 
> Matthew,
> 
> Did you really mean EnterVirtualMode (not ExitBootServices?)

I think I actually meant SetVirtualAddressMap() :)

> In one of your earlier emails you mentioned the issue is that linux makes
> regions NX.  That would cause problems if FW tried to execute a region
> we just reserved.  Unfortunately, i'm not seeing where the kernel is
> doing this for crash kernel memory.  Assuming it is making it NX, can
> we defer that part?  Or if its not, do we have a problem w/ crash kernel
> reservation at all?

I don't think we explicitly do that at any point for crash kernel 
regions. The boot services regions get toggled by efi_set_executable().

> Interesting questions, but as I don't have access to a system that has
> the firmware defects encountered when efi_reserve_boot_services, it makes
> it difficult to test that i don't break them.  Hence, the appealing nature
> of quirks.  Don't have to worry about breaking other platforms as they
> continue to operate same as before.

Yeah. The problem is that some users may want kdump while still having 
broken firmware, so a solution that works for them is much more 
appealing than one which involves manually maintaining a list of 
verified systems...

-- 
Matthew Garrett | mjg59@...f.ucam.org
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