ALSA: pcm: Add copy ops with iov_iter

iov_iter is a universal interface to copy the data chunk from/to
user-space and kernel in a unified manner.  This API can fit for ALSA
PCM copy ops, too; we had to split to copy_user and copy_kernel in the
past, and those can be unified to a single ops with iov_iter.

This patch adds a new PCM copy ops that passes iov_iter for copying
both kernel and user-space in the same way.  This patch touches only
the ALSA PCM core part, and the actual users will be replaced in the
following patches.

The expansion of iov_iter is done in the PCM core right before calling
each copy callback.  It's a bit suboptimal, but I took this now as
it's the most straightforward replacement.  The more conversion to
iov_iter in the caller side is a TODO for future.

As of now, the old copy_user and copy_kernel ops are still kept.
Once after all users are converted, we'll drop the old copy_user and
copy_kernel ops, too.

Link: https://lore.kernel.org/r/20230815190136.8987-3-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

include/sound/pcm.h

@@ -16,6 +16,7 @@
 #include <linux/bitops.h>
 #include <linux/pm_qos.h>
 #include <linux/refcount.h>
+#include <linux/uio.h>
 
 #define snd_pcm_substream_chip(substream) ((substream)->private_data)
 #define snd_pcm_chip(pcm) ((pcm)->private_data)
@@ -68,6 +69,8 @@ struct snd_pcm_ops {
 			struct snd_pcm_audio_tstamp_report *audio_tstamp_report);
 	int (*fill_silence)(struct snd_pcm_substream *substream, int channel,
 			    unsigned long pos, unsigned long bytes);
+	int (*copy)(struct snd_pcm_substream *substream, int channel,
+		    unsigned long pos, struct iov_iter *iter, unsigned long bytes);
 	int (*copy_user)(struct snd_pcm_substream *substream, int channel,
 			 unsigned long pos, void __user *buf,
 			 unsigned long bytes);

sound/core/pcm_lib.c

@@ -1973,10 +1973,11 @@ static int wait_for_avail(struct snd_pcm_substream *substream,
 	
 typedef int (*pcm_transfer_f)(struct snd_pcm_substream *substream,
 			      int channel, unsigned long hwoff,
-			      void *buf, unsigned long bytes);
+			      struct iov_iter *iter, unsigned long bytes);
 
 typedef int (*pcm_copy_f)(struct snd_pcm_substream *, snd_pcm_uframes_t, void *,
-			  snd_pcm_uframes_t, snd_pcm_uframes_t, pcm_transfer_f);
+			  snd_pcm_uframes_t, snd_pcm_uframes_t, pcm_transfer_f,
+			  bool);
 
 /* calculate the target DMA-buffer position to be written/read */
 static void *get_dma_ptr(struct snd_pcm_runtime *runtime,
@@ -1986,32 +1987,24 @@ static void *get_dma_ptr(struct snd_pcm_runtime *runtime,
 		channel * (runtime->dma_bytes / runtime->channels);
 }
 
-/* default copy_user ops for write; used for both interleaved and non- modes */
+/* default copy ops for write; used for both interleaved and non- modes */
 static int default_write_copy(struct snd_pcm_substream *substream,
 			      int channel, unsigned long hwoff,
-			      void *buf, unsigned long bytes)
+			      struct iov_iter *iter, unsigned long bytes)
 {
-	if (copy_from_user(get_dma_ptr(substream->runtime, channel, hwoff),
+	if (!copy_from_iter(get_dma_ptr(substream->runtime, channel, hwoff),
-			   (void __user *)buf, bytes))
+			    bytes, iter))
 		return -EFAULT;
 	return 0;
 }
 
-/* default copy_kernel ops for write */
-static int default_write_copy_kernel(struct snd_pcm_substream *substream,
-				     int channel, unsigned long hwoff,
-				     void *buf, unsigned long bytes)
-{
-	memcpy(get_dma_ptr(substream->runtime, channel, hwoff), buf, bytes);
-	return 0;
-}
-
 /* fill silence instead of copy data; called as a transfer helper
  * from __snd_pcm_lib_write() or directly from noninterleaved_copy() when
  * a NULL buffer is passed
  */
 static int fill_silence(struct snd_pcm_substream *substream, int channel,
-			unsigned long hwoff, void *buf, unsigned long bytes)
+			unsigned long hwoff, struct iov_iter *iter,
+			unsigned long bytes)
 {
 	struct snd_pcm_runtime *runtime = substream->runtime;
 
@@ -2027,25 +2020,54 @@ static int fill_silence(struct snd_pcm_substream *substream, int channel,
 	return 0;
 }
 
-/* default copy_user ops for read; used for both interleaved and non- modes */
+/* default copy ops for read; used for both interleaved and non- modes */
 static int default_read_copy(struct snd_pcm_substream *substream,
 			     int channel, unsigned long hwoff,
-			     void *buf, unsigned long bytes)
+			     struct iov_iter *iter, unsigned long bytes)
 {
-	if (copy_to_user((void __user *)buf,
+	if (!copy_to_iter(get_dma_ptr(substream->runtime, channel, hwoff),
-			 get_dma_ptr(substream->runtime, channel, hwoff),
+			  bytes, iter))
-			 bytes))
 		return -EFAULT;
 	return 0;
 }
 
-/* default copy_kernel ops for read */
+/* a wrapper for calling old copy_kernel or copy_user ops */
-static int default_read_copy_kernel(struct snd_pcm_substream *substream,
+static int call_old_copy(struct snd_pcm_substream *substream,
 			 int channel, unsigned long hwoff,
-				    void *buf, unsigned long bytes)
+			 struct iov_iter *iter, unsigned long bytes)
 {
-	memcpy(buf, get_dma_ptr(substream->runtime, channel, hwoff), bytes);
+	if (iov_iter_is_kvec(iter))
-	return 0;
+		return substream->ops->copy_kernel(substream, channel, hwoff,
+						   iter_iov_addr(iter), bytes);
+	else
+		return substream->ops->copy_user(substream, channel, hwoff,
+						 iter_iov_addr(iter), bytes);
+}
+
+/* call transfer with the filled iov_iter */
+static int do_transfer(struct snd_pcm_substream *substream, int c,
+		       unsigned long hwoff, void *data, unsigned long bytes,
+		       pcm_transfer_f transfer, bool in_kernel)
+{
+	struct iov_iter iter;
+	int err, type;
+
+	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
+		type = ITER_SOURCE;
+	else
+		type = ITER_DEST;
+
+	if (in_kernel) {
+		struct kvec kvec = { data, bytes };
+
+		iov_iter_kvec(&iter, type, &kvec, 1, bytes);
+		return transfer(substream, c, hwoff, &iter, bytes);
+	}
+
+	err = import_ubuf(type, (__force void __user *)data, bytes, &iter);
+	if (err)
+		return err;
+	return transfer(substream, c, hwoff, &iter, bytes);
 }
 
 /* call transfer function with the converted pointers and sizes;
@@ -2055,7 +2077,8 @@ static int interleaved_copy(struct snd_pcm_substream *substream,
 			    snd_pcm_uframes_t hwoff, void *data,
 			    snd_pcm_uframes_t off,
 			    snd_pcm_uframes_t frames,
-			    pcm_transfer_f transfer)
+			    pcm_transfer_f transfer,
+			    bool in_kernel)
 {
 	struct snd_pcm_runtime *runtime = substream->runtime;
 
@@ -2063,7 +2086,9 @@ static int interleaved_copy(struct snd_pcm_substream *substream,
 	hwoff = frames_to_bytes(runtime, hwoff);
 	off = frames_to_bytes(runtime, off);
 	frames = frames_to_bytes(runtime, frames);
-	return transfer(substream, 0, hwoff, data + off, frames);
+
+	return do_transfer(substream, 0, hwoff, data + off, frames, transfer,
+			   in_kernel);
 }
 
 /* call transfer function with the converted pointers and sizes for each
@@ -2073,7 +2098,8 @@ static int noninterleaved_copy(struct snd_pcm_substream *substream,
 			       snd_pcm_uframes_t hwoff, void *data,
 			       snd_pcm_uframes_t off,
 			       snd_pcm_uframes_t frames,
-			       pcm_transfer_f transfer)
+			       pcm_transfer_f transfer,
+			       bool in_kernel)
 {
 	struct snd_pcm_runtime *runtime = substream->runtime;
 	int channels = runtime->channels;
@@ -2091,8 +2117,8 @@ static int noninterleaved_copy(struct snd_pcm_substream *substream,
 		if (!data || !*bufs)
 			err = fill_silence(substream, c, hwoff, NULL, frames);
 		else
-			err = transfer(substream, c, hwoff, *bufs + off,
+			err = do_transfer(substream, c, hwoff, *bufs + off,
-				       frames);
+					  frames, transfer, in_kernel);
 		if (err < 0)
 			return err;
 	}
@@ -2108,10 +2134,10 @@ static int fill_silence_frames(struct snd_pcm_substream *substream,
 	if (substream->runtime->access == SNDRV_PCM_ACCESS_RW_INTERLEAVED ||
 	    substream->runtime->access == SNDRV_PCM_ACCESS_MMAP_INTERLEAVED)
 		return interleaved_copy(substream, off, NULL, 0, frames,
-					fill_silence);
+					fill_silence, true);
 	else
 		return noninterleaved_copy(substream, off, NULL, 0, frames,
-					   fill_silence);
+					   fill_silence, true);
 }
 
 /* sanity-check for read/write methods */
@@ -2121,7 +2147,7 @@ static int pcm_sanity_check(struct snd_pcm_substream *substream)
 	if (PCM_RUNTIME_CHECK(substream))
 		return -ENXIO;
 	runtime = substream->runtime;
-	if (snd_BUG_ON(!substream->ops->copy_user && !runtime->dma_area))
+	if (snd_BUG_ON(!substream->ops->copy && !substream->ops->copy_user && !runtime->dma_area))
 		return -EINVAL;
 	if (runtime->state == SNDRV_PCM_STATE_OPEN)
 		return -EBADFD;
@@ -2226,15 +2252,12 @@ snd_pcm_sframes_t __snd_pcm_lib_xfer(struct snd_pcm_substream *substream,
 			transfer = fill_silence;
 		else
 			return -EINVAL;
-	} else if (in_kernel) {
-		if (substream->ops->copy_kernel)
-			transfer = substream->ops->copy_kernel;
-		else
-			transfer = is_playback ?
-				default_write_copy_kernel : default_read_copy_kernel;
 	} else {
-		if (substream->ops->copy_user)
+		if (substream->ops->copy)
-			transfer = (pcm_transfer_f)substream->ops->copy_user;
+			transfer = substream->ops->copy;
+		else if ((in_kernel && substream->ops->copy_kernel) ||
+			 (!in_kernel && substream->ops->copy_user))
+			transfer = call_old_copy;
 		else
 			transfer = is_playback ?
 				default_write_copy : default_read_copy;
@@ -2307,7 +2330,7 @@ snd_pcm_sframes_t __snd_pcm_lib_xfer(struct snd_pcm_substream *substream,
 		if (!is_playback)
 			snd_pcm_dma_buffer_sync(substream, SNDRV_DMA_SYNC_CPU);
 		err = writer(substream, appl_ofs, data, offset, frames,
-			     transfer);
+			     transfer, in_kernel);
 		if (is_playback)
 			snd_pcm_dma_buffer_sync(substream, SNDRV_DMA_SYNC_DEVICE);
 		snd_pcm_stream_lock_irq(substream);

sound/core/pcm_native.c

@@ -809,7 +809,7 @@ static int snd_pcm_hw_params(struct snd_pcm_substream *substream,
 		runtime->boundary *= 2;
 
 	/* clear the buffer for avoiding possible kernel info leaks */
-	if (runtime->dma_area && !substream->ops->copy_user) {
+	if (runtime->dma_area && !substream->ops->copy && !substream->ops->copy_user) {
 		size_t size = runtime->dma_bytes;
 
 		if (runtime->info & SNDRV_PCM_INFO_MMAP)