[PATCH V1] accel/amdxdna: Support read-only user-pointer BO mappings

[Lizhi Hou]

From: Max Zhen <max.zhen@xxxxxxx>

Update the amdxdna user-pointer (ubuf) BO path to support creating buffer
objects from read-only user mappings.

Detect read-only VMAs by checking VMA permissions across all user virtual
address ranges associated with the BO. When all entries are read-only, pin
user pages without FOLL_WRITE and export the resulting dmabuf as read-only
(O_RDONLY).

This allows userptr BOs backed by read-only mappings to be safely imported
and used without requiring write access, which was previously rejected due
to unconditional FOLL_WRITE usage.

Signed-off-by: Max Zhen <max.zhen@xxxxxxx>
Signed-off-by: Lizhi Hou <lizhi.hou@xxxxxxx>
---
 drivers/accel/amdxdna/amdxdna_ubuf.c | 30 ++++++++++++++++++++++++++--
 1 file changed, 28 insertions(+), 2 deletions(-)

diff --git a/drivers/accel/amdxdna/amdxdna_ubuf.c b/drivers/accel/amdxdna/amdxdna_ubuf.c
index 4c0647057759..1a0e2a274170 100644
--- a/drivers/accel/amdxdna/amdxdna_ubuf.c
+++ b/drivers/accel/amdxdna/amdxdna_ubuf.c
@@ -125,6 +125,27 @@ static const struct dma_buf_ops amdxdna_ubuf_dmabuf_ops = {
 	.vunmap = amdxdna_ubuf_vunmap,
 };
 
+static int readonly_va_entry(struct amdxdna_drm_va_entry *va_ent)
+{
+	struct mm_struct *mm = current->mm;
+	struct vm_area_struct *vma;
+	int ret;
+
+	mmap_read_lock(mm);
+
+	vma = find_vma(mm, va_ent->vaddr);
+	if (!vma ||
+	    vma->vm_start > va_ent->vaddr ||
+	    vma->vm_end < va_ent->vaddr ||
+	    vma->vm_end - va_ent->vaddr < va_ent->len)
+		ret = -ENOENT;
+	else
+		ret = vma->vm_flags & VM_WRITE ? 0 : 1;
+
+	mmap_read_unlock(mm);
+	return ret;
+}
+
 struct dma_buf *amdxdna_get_ubuf(struct drm_device *dev,
 				 u32 num_entries, void __user *va_entries)
 {
@@ -134,6 +155,7 @@ struct dma_buf *amdxdna_get_ubuf(struct drm_device *dev,
 	struct amdxdna_ubuf_priv *ubuf;
 	u32 npages, start = 0;
 	struct dma_buf *dbuf;
+	bool readonly = true;
 	int i, ret;
 	DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
 
@@ -172,6 +194,10 @@ struct dma_buf *amdxdna_get_ubuf(struct drm_device *dev,
 			ret = -EINVAL;
 			goto free_ent;
 		}
+
+		/* Pin pages as writable as long as not all entries are read-only. */
+		if (readonly && readonly_va_entry(&va_ent[i]) != 1)
+			readonly = false;
 	}
 
 	ubuf->nr_pages = exp_info.size >> PAGE_SHIFT;
@@ -194,7 +220,7 @@ struct dma_buf *amdxdna_get_ubuf(struct drm_device *dev,
 		npages = va_ent[i].len >> PAGE_SHIFT;
 
 		ret = pin_user_pages_fast(va_ent[i].vaddr, npages,
-					  FOLL_WRITE | FOLL_LONGTERM,
+					  (readonly ? 0 : FOLL_WRITE) | FOLL_LONGTERM,
 					  &ubuf->pages[start]);
 		if (ret >= 0) {
 			start += ret;
@@ -211,7 +237,7 @@ struct dma_buf *amdxdna_get_ubuf(struct drm_device *dev,
 
 	exp_info.ops = &amdxdna_ubuf_dmabuf_ops;
 	exp_info.priv = ubuf;
-	exp_info.flags = O_RDWR | O_CLOEXEC;
+	exp_info.flags = (readonly ? O_RDONLY : O_RDWR) | O_CLOEXEC;
 
 	dbuf = dma_buf_export(&exp_info);
 	if (IS_ERR(dbuf)) {
-- 
2.34.1