drm/xe/xe_pagefault: Disallow writes to read-only VMAs

The page fault handler should reject write/atomic access to read only
VMAs.  Add code to handle this in xe_pagefault_service after the VMA
lookup.

v2:
- Apply max line length (Matthew)

Fixes: fb544b8 ("drm/xe: Implement xe_pagefault_queue_work")
Signed-off-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
Suggested-by: Matthew Brost <matthew.brost@intel.com>
Cc: Shuicheng Lin <shuicheng.lin@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>

Author: Jonathan-Cavitt

drivers/gpu/drm/xe/xe_pagefault.c

@@ -187,6 +187,12 @@ static int xe_pagefault_service(struct xe_pagefault *pf)
 		goto unlock_vm;
 	}
 
+	if (xe_vma_read_only(vma) &&
+	    pf->consumer.access_type != XE_PAGEFAULT_ACCESS_TYPE_READ) {
+		err = -EPERM;
+		goto unlock_vm;
+	}
+
 	atomic = xe_pagefault_access_is_atomic(pf->consumer.access_type);
 
 	if (xe_vma_is_cpu_addr_mirror(vma))