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

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Date:	Tue, 24 Nov 2009 01:48:54 -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 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).

gart iommu workaround will allocate 64M by default.

fail config: like system with 512g and sparse mem, and vmmap.

YH
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