accel/amdxdna: Support read-only user-pointer BO mappings

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.

Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Signed-off-by: Max Zhen <max.zhen@amd.com>
Signed-off-by: Lizhi Hou <lizhi.hou@amd.com>
Link: https://patch.msgid.link/20260331172635.3275296-1-lizhi.hou@amd.com

diff --git a/drivers/accel/amdxdna/amdxdna_ubuf.c b/drivers/accel/amdxdna/amdxdna_ubuf.c
index 4c0647057759f82c472587b9cebf14bbadf1f967..3769210c55ccd62550fbf7e1664bc1a6259df513 100644 (file)
--- a/drivers/accel/amdxdna/amdxdna_ubuf.c
+++ b/drivers/accel/amdxdna/amdxdna_ubuf.c
@@ -125,6 +125,26 @@ 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 < 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 +154,7 @@ 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 +193,10 @@ 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 +219,7 @@ 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 +236,7 @@ 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)) {