drm/i915: Require the vm mutex for i915_vma_bind()

Protect updates of struct i915_vma flags and async binding / unbinding
with the vm::mutex. This means that i915_vma_bind() needs to assert
vm::mutex held. In order to make that possible drop the caching of
kmap_atomic() maps around i915_vma_bind().

An alternative would be to use kmap_local() but since we block cpu
unplugging during sleeps inside kmap_local() sections this may have
unwanted side-effects. Particularly since we might wait for gpu while
holding the vm mutex.

This change may theoretically increase execbuf cpu-usage on snb, but
at least on non-highmem systems that increase should be very small.

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211221200050.436316-5-thomas.hellstrom@linux.intel.com

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
index 3ff95e54a353..29a858c53bdd 100644
--- a/drivers/gpu/drm/i915/i915_vma.c
+++ b/drivers/gpu/drm/i915/i915_vma.c
@@ -393,6 +393,7 @@ int i915_vma_bind(struct i915_vma *vma,
 	u32 bind_flags;
 	u32 vma_flags;
 
+	lockdep_assert_held(&vma->vm->mutex);
 	GEM_BUG_ON(!drm_mm_node_allocated(&vma->node));
 	GEM_BUG_ON(vma->size > vma->node.size);