This patch attempted to work around a DMA issue involving Xen, but
causes subtle kernel memory corruption.
When I brought up this patch in the XenDevel matrix channel, I was
told that it had been requested by the Qubes OS developers because
they were trying to fix an issue where the sound stack would fail
after a few hours of uptime. They wound up disabling SG buffering
entirely instead as a workaround.
Accordingly, I propose that we should revert this workaround patch,
since it causes kernel memory corruption and that the ALSA and Xen
communities should collaborate on fixing the underlying problem in
such a way that SG buffering works correctly under Xen.
This reverts commit 53466ebdec614f915c691809b0861acecb941e30.
Signed-off-by: Ariadne Conill <ariadne@ariadne.space>
Cc: stable@xxxxxxxxxxxxxxx
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
Cc: alsa-devel@xxxxxxxxxxxxxxxx
Cc: Takashi Iwai <tiwai@xxxxxxx>
---
sound/core/memalloc.c | 87 +++++++++----------------------------------
1 file changed, 18 insertions(+), 69 deletions(-)
diff --git a/sound/core/memalloc.c b/sound/core/memalloc.c
index f901504b5afc..81025f50a542 100644
--- a/sound/core/memalloc.c
+++ b/sound/core/memalloc.c
@@ -541,15 +541,16 @@ static void *snd_dma_noncontig_alloc(struct snd_dma_buffer *dmab, size_t size)
struct sg_table *sgt;
void *p;
-#ifdef CONFIG_SND_DMA_SGBUF
- if (cpu_feature_enabled(X86_FEATURE_XENPV))
- return snd_dma_sg_fallback_alloc(dmab, size);
-#endif
sgt = dma_alloc_noncontiguous(dmab->dev.dev, size, dmab->dev.dir,
DEFAULT_GFP, 0);
#ifdef CONFIG_SND_DMA_SGBUF
- if (!sgt && !get_dma_ops(dmab->dev.dev))
+ if (!sgt && !get_dma_ops(dmab->dev.dev)) {
+ if (dmab->dev.type == SNDRV_DMA_TYPE_DEV_WC_SG)
+ dmab->dev.type = SNDRV_DMA_TYPE_DEV_WC_SG_FALLBACK;
+ else
+ dmab->dev.type = SNDRV_DMA_TYPE_DEV_SG_FALLBACK;
return snd_dma_sg_fallback_alloc(dmab, size);
+ }
#endif
if (!sgt)
return NULL;
@@ -716,38 +717,19 @@ static const struct snd_malloc_ops snd_dma_sg_wc_ops = {
/* Fallback SG-buffer allocations for x86 */
struct snd_dma_sg_fallback {
- bool use_dma_alloc_coherent;
size_t count;
struct page **pages;
- /* DMA address array; the first page contains #pages in ~PAGE_MASK */
- dma_addr_t *addrs;
};
static void __snd_dma_sg_fallback_free(struct snd_dma_buffer *dmab,
struct snd_dma_sg_fallback *sgbuf)
{
- size_t i, size;
-
- if (sgbuf->pages && sgbuf->addrs) {
- i = 0;
- while (i < sgbuf->count) {
- if (!sgbuf->pages[i] || !sgbuf->addrs[i])
- break;
- size = sgbuf->addrs[i] & ~PAGE_MASK;
- if (WARN_ON(!size))
- break;
- if (sgbuf->use_dma_alloc_coherent)
- dma_free_coherent(dmab->dev.dev, size << PAGE_SHIFT,
- page_address(sgbuf->pages[i]),
- sgbuf->addrs[i] & PAGE_MASK);
- else
- do_free_pages(page_address(sgbuf->pages[i]),
- size << PAGE_SHIFT, false);
- i += size;
- }
- }
+ bool wc = dmab->dev.type == SNDRV_DMA_TYPE_DEV_WC_SG_FALLBACK;
+ size_t i;
+
+ for (i = 0; i < sgbuf->count && sgbuf->pages[i]; i++)
+ do_free_pages(page_address(sgbuf->pages[i]), PAGE_SIZE, wc);
kvfree(sgbuf->pages);
- kvfree(sgbuf->addrs);
kfree(sgbuf);
}
@@ -756,36 +738,24 @@ static void *snd_dma_sg_fallback_alloc(struct snd_dma_buffer *dmab, size_t size)
struct snd_dma_sg_fallback *sgbuf;
struct page **pagep, *curp;
size_t chunk, npages;
- dma_addr_t *addrp;
dma_addr_t addr;
void *p;
-
- /* correct the type */
- if (dmab->dev.type == SNDRV_DMA_TYPE_DEV_SG)
- dmab->dev.type = SNDRV_DMA_TYPE_DEV_SG_FALLBACK;
- else if (dmab->dev.type == SNDRV_DMA_TYPE_DEV_WC_SG)
- dmab->dev.type = SNDRV_DMA_TYPE_DEV_WC_SG_FALLBACK;
+ bool wc = dmab->dev.type == SNDRV_DMA_TYPE_DEV_WC_SG_FALLBACK;
sgbuf = kzalloc(sizeof(*sgbuf), GFP_KERNEL);
if (!sgbuf)
return NULL;
- sgbuf->use_dma_alloc_coherent = cpu_feature_enabled(X86_FEATURE_XENPV);
size = PAGE_ALIGN(size);
sgbuf->count = size >> PAGE_SHIFT;
sgbuf->pages = kvcalloc(sgbuf->count, sizeof(*sgbuf->pages), GFP_KERNEL);
- sgbuf->addrs = kvcalloc(sgbuf->count, sizeof(*sgbuf->addrs), GFP_KERNEL);
- if (!sgbuf->pages || !sgbuf->addrs)
+ if (!sgbuf->pages)
goto error;
pagep = sgbuf->pages;
- addrp = sgbuf->addrs;
- chunk = (PAGE_SIZE - 1) << PAGE_SHIFT; /* to fit in low bits in addrs */
+ chunk = size;
while (size > 0) {
chunk = min(size, chunk);
- if (sgbuf->use_dma_alloc_coherent)
- p = dma_alloc_coherent(dmab->dev.dev, chunk, &addr, DEFAULT_GFP);
- else
- p = do_alloc_pages(dmab->dev.dev, chunk, &addr, false);
+ p = do_alloc_pages(dmab->dev.dev, chunk, &addr, wc);
if (!p) {
if (chunk <= PAGE_SIZE)
goto error;
@@ -797,25 +767,17 @@ static void *snd_dma_sg_fallback_alloc(struct snd_dma_buffer *dmab, size_t size)
size -= chunk;
/* fill pages */
npages = chunk >> PAGE_SHIFT;
- *addrp = npages; /* store in lower bits */
curp = virt_to_page(p);
- while (npages--) {
+ while (npages--)
*pagep++ = curp++;
- *addrp++ |= addr;
- addr += PAGE_SIZE;
- }
}
p = vmap(sgbuf->pages, sgbuf->count, VM_MAP, PAGE_KERNEL);
if (!p)
goto error;
-
- if (dmab->dev.type == SNDRV_DMA_TYPE_DEV_WC_SG_FALLBACK)
- set_pages_array_wc(sgbuf->pages, sgbuf->count);
-
dmab->private_data = sgbuf;
/* store the first page address for convenience */
- dmab->addr = sgbuf->addrs[0] & PAGE_MASK;
+ dmab->addr = snd_sgbuf_get_addr(dmab, 0);
return p;
error:
@@ -825,23 +787,10 @@ static void *snd_dma_sg_fallback_alloc(struct snd_dma_buffer *dmab, size_t size)
static void snd_dma_sg_fallback_free(struct snd_dma_buffer *dmab)
{
- struct snd_dma_sg_fallback *sgbuf = dmab->private_data;
-
- if (dmab->dev.type == SNDRV_DMA_TYPE_DEV_WC_SG_FALLBACK)
- set_pages_array_wb(sgbuf->pages, sgbuf->count);
vunmap(dmab->area);
__snd_dma_sg_fallback_free(dmab, dmab->private_data);
}
-static dma_addr_t snd_dma_sg_fallback_get_addr(struct snd_dma_buffer *dmab,
- size_t offset)
-{
- struct snd_dma_sg_fallback *sgbuf = dmab->private_data;
- size_t index = offset >> PAGE_SHIFT;
-
- return (sgbuf->addrs[index] & PAGE_MASK) | (offset & ~PAGE_MASK);
-}
-
static int snd_dma_sg_fallback_mmap(struct snd_dma_buffer *dmab,
struct vm_area_struct *area)
{
@@ -856,8 +805,8 @@ static const struct snd_malloc_ops snd_dma_sg_fallback_ops = {
.alloc = snd_dma_sg_fallback_alloc,
.free = snd_dma_sg_fallback_free,
.mmap = snd_dma_sg_fallback_mmap,
- .get_addr = snd_dma_sg_fallback_get_addr,
/* reuse vmalloc helpers */
+ .get_addr = snd_dma_vmalloc_get_addr,
.get_page = snd_dma_vmalloc_get_page,
.get_chunk_size = snd_dma_vmalloc_get_chunk_size,
};
--
2.39.2
