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SubjectRe: [PATCH]: PCI: GART iommu alignment fixes [v2]


FUJITA Tomonori wrote:
> On Mon, 28 Jul 2008 15:23:35 -0700
> Jesse Barnes <jbarnes@virtuousgeek.org> wrote:
>
>
>> On Wednesday, July 23, 2008 4:14 pm FUJITA Tomonori wrote:
>>
>>> On Thu, 24 Jul 2008 00:10:33 +0200
>>>
>>> Joerg Roedel <joro@8bytes.org> wrote:
>>>
>>>> On Wed, Jul 23, 2008 at 07:19:43AM -0400, Prarit Bhargava wrote:
>>>>
>>>>> pci_alloc_consistent/dma_alloc_coherent does not return size aligned
>>>>> addresses.
>>>>>
>>>>> >From Documentation/DMA-mapping.txt:
>>>>>
>>>>> "pci_alloc_consistent returns two values: the virtual address which you
>>>>> can use to access it from the CPU and dma_handle which you pass to the
>>>>> card.
>>>>>
>>>>> The cpu return address and the DMA bus master address are both
>>>>> guaranteed to be aligned to the smallest PAGE_SIZE order which
>>>>> is greater than or equal to the requested size. This invariant
>>>>> exists (for example) to guarantee that if you allocate a chunk
>>>>> which is smaller than or equal to 64 kilobytes, the extent of the
>>>>> buffer you receive will not cross a 64K boundary."
>>>>>
>>>> Interesting. Have you experienced any problems because of that
>>>> misbehavior in the GART code? AMD IOMMU currently also violates this
>>>> requirement. I will send a patch to fix that there too.
>>>>
>>> IIRC, only PARISC and POWER IOMMUs follow the above rule. So I also
>>> wondered what problem he hit.
>>>
>> Prarit, what's the latest here? The v3 patch I have from you doesn't apply to
>> my tree but it looks like a good fix. Care to send me a new patch against my
>> for-linus branch?
>>
>
> I'm not sure how the following cast to 'unsigned long long' fixes
> something on X86_64.
>
>

You can write a very simple module that kmalloc's a pci_dev, sets up
some trivial values for the dev, and then calls pci_alloc_consistent.
You will panic 100% of the time because 'dma_get_seg_boundary(dev) + 1'
overflows an unsigned long.

>> Signed-off-by: Prarit Bhargava <prarit@redhat.com>
>>
>> diff --git a/arch/x86/kernel/pci-gart_64.c b/arch/x86/kernel/pci-gart_64.c
>> index 744126e..d3eb527 100644
>> --- a/arch/x86/kernel/pci-gart_64.c
>> +++ b/arch/x86/kernel/pci-gart_64.c
>> @@ -85,7 +85,8 @@ AGPEXTERN __u32 *agp_gatt_table;
>> static unsigned long next_bit; /* protected by iommu_bitmap_lock */
>> static int need_flush; /* global flush state. set for each gart wrap */
>>
>> -static unsigned long alloc_iommu(struct device *dev, int size)
>> +static unsigned long alloc_iommu(struct device *dev, int size,
>> + unsigned long mask)
>> {
>> unsigned long offset, flags;
>> unsigned long boundary_size;
>> @@ -93,16 +94,17 @@ static unsigned long alloc_iommu(struct device *dev, int size)
>>
>> base_index = ALIGN(iommu_bus_base & dma_get_seg_boundary(dev),
>> PAGE_SIZE) >> PAGE_SHIFT;
>> - boundary_size = ALIGN(dma_get_seg_boundary(dev) + 1,
>> + boundary_size = ALIGN((unsigned long long)dma_get_seg_boundary(dev) + 1,
>> PAGE_SIZE) >> PAGE_SHIFT;
>>
>
> I don't think that the following code works since the size is not
> always a power of 2.
>



>
>
>> @@ -265,7 +268,7 @@ static dma_addr_t dma_map_area(struct device *dev, dma_addr_t phys_mem,
>> static dma_addr_t
>> gart_map_simple(struct device *dev, phys_addr_t paddr, size_t size, int dir)
>> {
>> - dma_addr_t map = dma_map_area(dev, paddr, size, dir);
>> + dma_addr_t map = dma_map_area(dev, paddr, size, dir, size - 1);
>>

Maybe I'm missing something -- what implies size has to be a power of two?

P.


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