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

[Prarit Bhargava]

FUJITA Tomonori wrote:
> On Mon, 28 Jul 2008 15:23:35 -0700
> Jesse Barnes <jbarnes@xxxxxxxxxxxxxxxx> wrote:
>
>   
> > On Wednesday, July 23, 2008 4:14 pm FUJITA Tomonori wrote:
> >     
> > > On Thu, 24 Jul 2008 00:10:33 +0200
> > >
> > > Joerg Roedel <joro@xxxxxxxxxx> 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@xxxxxxxxxx>
> >
> > 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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