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

[Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>]

On Thu, Feb 02, 2017 at 12:11:29PM +0000, Tvrtko Ursulin wrote:
> 
> 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
> >occurred.
> >
> >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 
> >b/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;
> > #ifdef CONFIG_SWIOTLB
> >-    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));
> >+            }
> >+    }
> > #endif
> >
> >     gfp = GFP_KERNEL | __GFP_HIGHMEM | __GFP_RECLAIMABLE;
> >
> 
> 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>

Pushed, I imagine this has been added to the list of sg cleanups you
have :)
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre

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