linux-kernel - Re: [PATCH] x86-64: disable the GART early v2

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Date:	Fri, 11 Jan 2008 00:34:46 -0800
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	"Andi Kleen" <ak@...e.de>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Christoph Lameter" <clameter@....com>, ebiederm@...ssion.com,
	"Thomas Gleixner" <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86-64: disable the GART early v2

On Jan 11, 2008 12:14 AM, Ingo Molnar <mingo@...e.hu> wrote:
>
> * Yinghai Lu <Yinghai.Lu@....COM> wrote:
>
> > --- a/arch/x86/kernel/aperture_64.c
> > +++ b/arch/x86/kernel/aperture_64.c
> > @@ -218,6 +218,73 @@ static __u32 __init search_agp_bridge(u32 *order, int *valid_agp)
> >       return 0;
> >  }
> >
> > +void __init early_gart_iommu_disable(void)
> > +{
> > +     /*
> > +      * disable it in case it is enabled before, esp for kexec/kdump,
> > +      * previous kernel already enable that. otherwise memset called
> > +      * by allocate_aperture/__alloc_bootmem_nopanic cause restart.
> > +      * or second kernel have different position for GART hole. and new
> > +      * kernel could use hole as RAM that is still used by GART set by
> > +      * first kernel
> > +      */
>
> hm, i'm wondering, instead of modifying the GART, why dont we simply
> _detect_ whatever GART settings we have inherited, and propagate that
> into our e820 maps? I.e. if there's inconsistency, then punch that out
> from the memory maps and just dont use that memory.
>
> that way it would not matter whether the GART settings came from a [old
> or crashing] Linux kernel that has not called gart_iommu_shutdown(), or
> whether it's a BIOS that has set up an aperture hole inconsistent with
> the memory map it passed. (or the memory map we _think_ i tried to pass
> us)
>
good, i will update the patch to check that hole with e820 map.

that also make code short so don't need to check if agp is there or not.

YH
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