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

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Message-ID: <4B0BA519.9090100@kernel.org>
Date:	Tue, 24 Nov 2009 01:19:21 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
CC:	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

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

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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