[PATCH v5 1/8] drm/xe/mmio_gem: forbid VMA split

[Matthew Auld <matthew.auld@intel.com>]

From: Ilia Levi <ilia.levi@intel.com>

The fault handler assumes it always operates on a VMA spanning the entire
GEM object. This does not hold when the VMA has been split, e.g. by a
partial munmap or mprotect. In that case the handler may map wrong
physical pages or cause SIGBUS.

Handle this by forbidding VMA split, as partial unmaps are not deemed
useful for MMIO GEMs.

Suggested-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Ilia Levi <ilia.levi@intel.com>
Fixes: 1ffcf8b8ae8a ("drm/xe: Support for mmap-ing mmio regions")
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
---
 drivers/gpu/drm/xe/xe_mmio_gem.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_mmio_gem.c b/drivers/gpu/drm/xe/xe_mmio_gem.c
index 3741ae60f532..d54477b93b6e 100644
--- a/drivers/gpu/drm/xe/xe_mmio_gem.c
+++ b/drivers/gpu/drm/xe/xe_mmio_gem.c
@@ -39,10 +39,20 @@ struct xe_mmio_gem {
 	phys_addr_t phys_addr;
 };
 
+static int xe_mmio_gem_vm_may_split(struct vm_area_struct *area, unsigned long addr)
+{
+	/*
+	 * Forbid splitting. Together with VM_DONTEXPAND, this keeps the VMA
+	 * matching the GEM object exactly.
+	 */
+	return -EINVAL;
+}
+
 static const struct vm_operations_struct vm_ops = {
 	.open = drm_gem_vm_open,
 	.close = drm_gem_vm_close,
 	.fault = xe_mmio_gem_vm_fault,
+	.may_split = xe_mmio_gem_vm_may_split,
 };
 
 static const struct drm_gem_object_funcs xe_mmio_gem_funcs = {
-- 
2.55.0