ALSA: memalloc: Workaround for Xen PV

We change recently the memalloc helper to use
dma_alloc_noncontiguous() and the fallback to get_pages().  Although
lots of issues with IOMMU (or non-IOMMU) have been addressed, but
there seems still a regression on Xen PV.  Interestingly, the only
proper way to work is use dma_alloc_coherent().  The use of
dma_alloc_coherent() for SG buffer was dropped as it's problematic on
IOMMU systems.  OTOH, Xen PV has a different way, and it's fine to use
the dma_alloc_coherent().

This patch is a workaround for Xen PV.  It consists of the following
changes:
- For Xen PV, use only the fallback allocation without
  dma_alloc_noncontiguous()
- In the fallback allocation, use dma_alloc_coherent();
  the DMA address from dma_alloc_coherent() is returned in get_addr
  ops
- The DMA addresses are stored in an array; the first entry stores the
  number of allocated pages in lower bits, which are referred at
  releasing pages again

Reported-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Tested-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Fixes: a8d302a0b770 ("ALSA: memalloc: Revive x86-specific WC page allocations again")
Fixes: 9736a325137b ("ALSA: memalloc: Don't fall back for SG-buffer with IOMMU")
Link: https://lore.kernel.org/r/87tu256lqs.wl-tiwai@suse.de
Link: https://lore.kernel.org/r/20230125153104.5527-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/core/memalloc.c b/sound/core/memalloc.c
index 81025f50a54229b080b9069b8003a891bb5e16a7..f901504b5afc17aef00a1bf1dafb277098624e1a 100644 (file)
--- a/sound/core/memalloc.c
+++ b/sound/core/memalloc.c
@@ -541,16 +541,15 @@ 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 (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;
+       if (!sgt && !get_dma_ops(dmab->dev.dev))
                return snd_dma_sg_fallback_alloc(dmab, size);
-       }
 #endif
        if (!sgt)
                return NULL;
@@ -717,19 +716,38 @@ 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)
 {
-       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);
+       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;
+               }
+       }
        kvfree(sgbuf->pages);
+       kvfree(sgbuf->addrs);
        kfree(sgbuf);
 }
 
@@ -738,24 +756,36 @@ 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;
-       bool wc = dmab->dev.type == SNDRV_DMA_TYPE_DEV_WC_SG_FALLBACK;
+
+       /* 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;
 
        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);
-       if (!sgbuf->pages)
+       sgbuf->addrs = kvcalloc(sgbuf->count, sizeof(*sgbuf->addrs), GFP_KERNEL);
+       if (!sgbuf->pages || !sgbuf->addrs)
                goto error;
 
        pagep = sgbuf->pages;
-       chunk = size;
+       addrp = sgbuf->addrs;
+       chunk = (PAGE_SIZE - 1) << PAGE_SHIFT; /* to fit in low bits in addrs */
        while (size > 0) {
                chunk = min(size, chunk);
-               p = do_alloc_pages(dmab->dev.dev, chunk, &addr, wc);
+               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);
                if (!p) {
                        if (chunk <= PAGE_SIZE)
                                goto error;
@@ -767,17 +797,25 @@ 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 = snd_sgbuf_get_addr(dmab, 0);
+       dmab->addr = sgbuf->addrs[0] & PAGE_MASK;
        return p;
 
  error:
@@ -787,10 +825,23 @@ 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)
 {
@@ -805,8 +856,8 @@ 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,
 };