Messages in this thread | | | Date | Tue, 4 Sep 2012 15:07:42 +0100 | From | Stefano Panella <> | Subject | Re: [Xen-devel] [PATCH 1/1] XEN: Use correct masking in xen_swiotlb_alloc_coherent. |
| |
On 08/31/2012 05:40 PM, Konrad Rzeszutek Wilk wrote: > On Fri, Aug 31, 2012 at 01:47:05PM +0100, David Vrabel wrote: >> On 31/08/12 10:57, Stefano Panella wrote: >>> When running 32-bit pvops-dom0 and a driver tries to allocate a coherent >>> DMA-memory the xen swiotlb-implementation returned memory beyond 4GB. >>> >>> This caused for example not working sound on a system with 4 GB and a 64-bit >>> compatible sound-card with sets the DMA-mask to 64bit. >>> >>> On bare-metal and the forward-ported xen-dom0 patches from OpenSuse a coherent >>> DMA-memory is always allocated inside the 32-bit address-range by calling >>> dma_alloc_coherent_mask. >> We should have the same behaviour under Xen as bare metal so: >> >> Acked-By: David Vrabel <david.vrabel@citrix.com> >> >> This does limit the DMA mask to 32-bits by passing it through an >> unsigned long, which seems a bit sneaky... > so is the issue that we are not casting it from 'u64' to 'u32' > (unsigned long) on 32-bit?
Yes. I do not completely understand why but I think on 32-bit kernel we need to cast dma_mask to u32. This is done automatically using dma_alloc_coherent_mask()
> >> Presumably the sound card is capable of handling 64 bit physical >> addresses (or it would break under 64-bit kernels) so it's not clear why >> this sound driver requires this restriction. >> >> Is there a bug in the sound driver or sound subsystem where it's >> truncating a dma_addr_t by assigning it to an unsigned long or similar? >> >>> --- a/drivers/xen/swiotlb-xen.c >>> +++ b/drivers/xen/swiotlb-xen.c >>> @@ -232,7 +232,7 @@ xen_swiotlb_alloc_coherent(struct device *hwdev, size_t size, >>> return ret; >>> >>> if (hwdev && hwdev->coherent_dma_mask) >>> - dma_mask = hwdev->coherent_dma_mask; >>> + dma_mask = dma_alloc_coherent_mask(hwdev, flags); >> Suggest >> >> if (hwdev) >> dma_mask = dma_alloc_coherent_mask(hwdev, flags)
I can change the patch like that if you like.
> Isn't that code just doing this: > atic inline unsigned long dma_alloc_coherent_mask(struct device *dev, > gfp_t gfp) > { > unsigned long dma_mask = 0; > > dma_mask = dev->coherent_dma_mask; > if (!dma_mask) > dma_mask = (gfp & GFP_DMA) ? DMA_BIT_MASK(24) : > DMA_BIT_MASK(32); > > return dma_mask; > } > > and in our code, the dma_mask by default is DMA_BIT_MASK(32): > > u64 dma_mask = DMA_BIT_MASK(32); > > So what I am missing?
I am not sure what you mean with "what am I missing?"
Current code looks like:
void * xen_swiotlb_alloc_coherent(struct device *hwdev, size_t size, dma_addr_t *dma_handle, gfp_t flags, struct dma_attrs *attrs) { void *ret; int order = get_order(size); u64 dma_mask = DMA_BIT_MASK(32); unsigned long vstart; phys_addr_t phys; dma_addr_t dev_addr;
/* * Ignore region specifiers - the kernel's ideas of * pseudo-phys memory layout has nothing to do with the * machine physical layout. We can't allocate highmem * because we can't return a pointer to it. */ flags &= ~(__GFP_DMA | __GFP_HIGHMEM);
if (dma_alloc_from_coherent(hwdev, size, dma_handle, &ret)) return ret;
vstart = __get_free_pages(flags, order); ret = (void *)vstart;
if (!ret) return ret;
if (hwdev && hwdev->coherent_dma_mask) dma_mask = hwdev->coherent_dma_mask;
So if hwdev->coherent_dma_mask is set to 0xffffffffffffffff our dma_mask will be u64 set to 0xffffffffffffffff even if we set it to DMA_BIT_MASK(32) previously.
I hope I am not getting this wrong and let me know if I should send an updated version of the patch including David V. change.
Regards,
Stefano
| |