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Re: [Xen-devel] [Intel-gfx] [PATCH] drm/i915: fix i915 running as dom0 under Xen

On 02/02/2017 09:47, Juergen Gross wrote:
Commit 920cf4194954ec ("drm/i915: Introduce an internal allocator for
disposable private objects") introduced a regression for the kernel
running as Xen dom0: when switching to graphics mode a GPU HANG

Reason seems to be a missing adaption similar to that done in
commit 7453c549f5f648 ("swiotlb: Export swiotlb_max_segment to users")
to i915_gem_object_get_pages_internal().

So limit the maximum page order to be used according to the maximum
swiotlb segment size instead to the complete swiotlb size.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Please consider for 4.10 as otherwise 4.10 will be unusable as Xen dom0
with i915 graphics.
 drivers/gpu/drm/i915/i915_gem_internal.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_internal.c 
index 4b3ff3e..d09c749 100644
--- a/drivers/gpu/drm/i915/i915_gem_internal.c
+++ b/drivers/gpu/drm/i915/i915_gem_internal.c
@@ -66,8 +66,16 @@ i915_gem_object_get_pages_internal(struct 
drm_i915_gem_object *obj)

        max_order = MAX_ORDER;
-       if (swiotlb_nr_tbl()) /* minimum max swiotlb size is IO_TLB_SEGSIZE */
-               max_order = min(max_order, ilog2(IO_TLB_SEGPAGES));
+       if (swiotlb_nr_tbl()) {
+               unsigned int max_segment;
+               max_segment = swiotlb_max_segment();
+               if (max_segment) {
+                       max_segment = max_t(unsigned int, max_segment,
+                                           PAGE_SIZE) >> PAGE_SHIFT;
+                       max_order = min(max_order, ilog2(max_segment));
+               }
+       }


Looks OK to me. We could bikeshed it to only use swiotlb_max_segment() which I think was the intention when that API was added but can leave that for the future.

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>



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