[PATCH 12/39] ALSA: pcm: use vm_insert_page() to map PCM status page

[Lorenzo Stoakes (ARM)]

There's no need to keep a fault handler around for this, instead map on
mmap.

While we're here, rename area to vma to be consistent.

This correctly makes the mapping a mixed map mapping.

This works towards establishing the invariant that only PFN mapped or mixed
map mappings may clear the VM_MAYWRITE flag. The status page mapping clears
VM_MAYWRITE, so it must be kernel-owned; the control page mapping remains
writable and is left fault-based.

The assumption is made that the struct pcm_mmap_status structure is at most
a page in size, which is asserted as a build bug.

This is safe to assume, as the size of the structure is 56 bytes at most.

Signed-off-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>
---
 sound/core/pcm_native.c | 37 ++++++++++++-------------------------
 1 file changed, 12 insertions(+), 25 deletions(-)

diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 62324282fcae..37a157d55832 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -3760,39 +3760,26 @@ static __poll_t snd_pcm_poll(struct file *file, poll_table *wait)
 /*
  * mmap status record
  */
-static vm_fault_t snd_pcm_mmap_status_fault(struct vm_fault *vmf)
+static int snd_pcm_mmap_status(struct snd_pcm_substream *substream, struct file *file,
+			       struct vm_area_struct *vma)
 {
-	struct snd_pcm_substream *substream = vmf->vma->vm_private_data;
+	const unsigned long size = vma->vm_end - vma->vm_start;
 	struct snd_pcm_runtime *runtime;
-	
-	if (substream == NULL)
-		return VM_FAULT_SIGBUS;
-	runtime = substream->runtime;
-	vmf->page = virt_to_page(runtime->status);
-	get_page(vmf->page);
-	return 0;
-}
+	struct page *page;
 
-static const struct vm_operations_struct snd_pcm_vm_ops_status =
-{
-	.fault =	snd_pcm_mmap_status_fault,
-};
+	BUILD_BUG_ON(sizeof(struct snd_pcm_mmap_status) > PAGE_SIZE);
 
-static int snd_pcm_mmap_status(struct snd_pcm_substream *substream, struct file *file,
-			       struct vm_area_struct *area)
-{
-	long size;
-	if (!(area->vm_flags & VM_READ))
+	if (!(vma->vm_flags & VM_READ))
 		return -EINVAL;
-	size = area->vm_end - area->vm_start;
-	if (size != PAGE_ALIGN(sizeof(struct snd_pcm_mmap_status)))
+	if (size != PAGE_SIZE)
 		return -EINVAL;
-	area->vm_ops = &snd_pcm_vm_ops_status;
-	area->vm_private_data = substream;
-	vm_flags_mod(area, VM_DONTEXPAND | VM_DONTDUMP,
+
+	vm_flags_mod(vma, VM_DONTEXPAND | VM_DONTDUMP,
 		     VM_WRITE | VM_MAYWRITE);
 
-	return 0;
+	runtime = substream->runtime;
+	page = virt_to_page(runtime->status);
+	return vm_insert_page(vma, vma->vm_start, page);
 }
 
 /*

-- 
2.55.0