linux-kernel - Re: [PATCH] x86: fix gart iommu using for amd 64 bit system

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Date:	Tue, 24 Nov 2009 18:35:12 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	yinghai@...nel.org
Cc:	fujita.tomonori@....ntt.co.jp, mingo@...e.hu, hpa@...or.com,
	tglx@...utronix.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: fix gart iommu using for amd 64 bit system

On Tue, 24 Nov 2009 01:19:21 -0800
Yinghai Lu <yinghai@...nel.org> wrote:

> FUJITA Tomonori wrote:
> > On Sat, 21 Nov 2009 20:24:52 -0800
> > Yinghai Lu <yinghai@...nel.org> wrote:
> > 
> >> amd 64 systems that
> >> 1. do not have  AGP
> >> 2. do not have IOMMU
> >> 3. mem > 4g
> >> 4. BIOS do not allocate  correct gart in NB.
> >> will leave them to use SWIOTLB forcely.
> > 
> > Sorry, I forgot about this GART workaround.
> > 
> > 
> >> Index: linux-2.6/arch/x86/kernel/pci-dma.c
> >> ===================================================================
> >> --- linux-2.6.orig/arch/x86/kernel/pci-dma.c
> >> +++ linux-2.6/arch/x86/kernel/pci-dma.c
> >> @@ -124,11 +124,12 @@ void __init pci_iommu_alloc(void)
> >>  	/* free the range so iommu could get some range less than 4G */
> >>  	dma32_free_bootmem();
> >>  #endif
> >> +	if (!swiotlb_force)
> >> +		gart_iommu_hole_init();
> >> +
> >>  	if (pci_swiotlb_init())
> >>  		return;
> >>  
> >> -	gart_iommu_hole_init();
> >> -
> >>  	detect_calgary();
> >>  
> >>  	detect_intel_iommu();
> > 
> > I prefer to detect all the IOMMU drivers in a consistent way;
> > detecting only GART before swioltb doesn't look nice.
> > 
> > As we did before, we could detect all the IOMMU driver before
> > swiotlb. However, I think that it's better to simply change
> > pci_swiotlb_init() not to steal the preallocate GART workaround memory.
> > 
> > btw, initializing swiotlb before IOMMU detection is useful to GART
> > too? If GART can't allocate the workaround memory, then the kernel
> > panic now. We can use swiotlb instead in that case?
> > 
> > =
> > From: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
> > Subject: [PATCH] x86: stop swiotlb stealing the GART workaround memory
> > 
> > swiotlb wrongly uses the GART workaround memory (for bad BIOS) that
> > dma32_reserv_bootmem allocates. We need to initialize swiotlb before
> > dma32_free_bootmem().
> > 
> > Signed-off-by: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
> > ---
> >  arch/x86/kernel/pci-dma.c |    6 +++++-
> >  1 files changed, 5 insertions(+), 1 deletions(-)
> > 
> > diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
> > index afcc58b..26fe2cd 100644
> > --- a/arch/x86/kernel/pci-dma.c
> > +++ b/arch/x86/kernel/pci-dma.c
> > @@ -120,11 +120,15 @@ static void __init dma32_free_bootmem(void)
> >  
> >  void __init pci_iommu_alloc(void)
> >  {
> > +	int use_swiotlb;
> > +
> > +	use_swiotlb = pci_swiotlb_init();
> > +
> >  #ifdef CONFIG_X86_64
> >  	/* free the range so iommu could get some range less than 4G */
> >  	dma32_free_bootmem();
> >  #endif
> > -	if (pci_swiotlb_init())
> > +	if (use_swiotlb)
> >  		return;
> >  
> >  	gart_iommu_hole_init();
> 
> pci_swiotlb_init need be called after dma32_free_bootmem
> otherwise it could fail for system with lots of memory and numa=off

Why? swiotlb needs just 64MB (and some) in DMA32.

swiotlb had been worked fine without that hack until 2.6.26?

Only broken GART needs that hack (and I think that it's better to move
that hack to GART code).


> so dma32_free_bootmem will work for gart_iommu_hole_init and pci_swiotlb_init..
> make sure they can get RAM < 4g.
> 
> also in gart_iommu_hole_init we need check swiotlb and !valid_agp...
> -       } else if (!valid_agp) {
> +       } else if (swiotlb && !valid_agp) {
> 
> otherwise the the workaround will be skipped...
> 
> YH
> --
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