[alsa-devel] [PATCH] sound: memalloc.h - fix wrong truncation of dma_addr_t

[Stefano Panella]

When running a 32bit kernel the hda_intel driver is still reporting
a 64bit dma_mask if the HW supports it.

>From sound/pci/hda/hda_intel.c:

        /* allow 64bit DMA address if supported by H/W */
        if ((gcap & ICH6_GCAP_64OK) && !pci_set_dma_mask(pci, DMA_BIT_MASK(64)))
                pci_set_consistent_dma_mask(pci, DMA_BIT_MASK(64));
        else {
                pci_set_dma_mask(pci, DMA_BIT_MASK(32));
                pci_set_consistent_dma_mask(pci, DMA_BIT_MASK(32));
        }

which means when there is a call to dma_alloc_coherent from
snd_malloc_dev_pages a machine address bigger than 32bit can be returned.
This can be true in particular if running  the 32bit kernel as a pv dom0
under the Xen Hypervisor or PAE on bare metal.

The problem is that when calling setup_bdle to program the BLE the
dma_addr_t returned from the dma_alloc_coherent is wrongly truncated
from snd_sgbuf_get_addr if running a 32bit kernel:

static inline dma_addr_t snd_sgbuf_get_addr(struct snd_dma_buffer *dmab,
                                           size_t offset)
{
        struct snd_sg_buf *sgbuf = dmab->private_data;
        dma_addr_t addr = sgbuf->table[offset >> PAGE_SHIFT].addr;
        addr &= PAGE_MASK;
        return addr + offset % PAGE_SIZE;
}

where PAGE_MASK in a 32bit kernel is zeroing the upper 32bit af addr.

Without this patch the HW will fetch the 32bit truncated address,
which is not the one obtained from dma_alloc_coherent and will result
to a non working audio but can corrupt host memory at a random location.

The current patch apply to v3.13-rc3-74-g6c843f5

Signed-off-by: Stefano Panella <stefano.panella at citrix.com>
Reviewed-by: Frediano Ziglio <frediano.ziglio at citrix.com>
---
 include/sound/memalloc.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/sound/memalloc.h b/include/sound/memalloc.h
index af99839..5f73785 100644
--- a/include/sound/memalloc.h
+++ b/include/sound/memalloc.h
@@ -108,7 +108,7 @@ static inline dma_addr_t snd_sgbuf_get_addr(struct snd_dma_buffer *dmab,
 {
 	struct snd_sg_buf *sgbuf = dmab->private_data;
 	dma_addr_t addr = sgbuf->table[offset >> PAGE_SHIFT].addr;
-	addr &= PAGE_MASK;
+	addr &= ~((dma_addr_t)PAGE_SIZE - 1);
 	return addr + offset % PAGE_SIZE;
 }
 
-- 
1.7.9.5