From: Chris Wilson <chris@chris-wilson.co.uk>
To: Juergen Gross <jgross@suse.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
dri-devel@lists.freedesktop.org,
intel-gfx <intel-gfx@lists.freedesktop.org>,
airlied@linux.ie, jani.nikula@linux.intel.com,
daniel.vetter@intel.com,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>
Subject: Re: i915 regression in kernel 4.10
Date: Mon, 19 Dec 2016 12:29:34 +0000 [thread overview]
Message-ID: <20161219122934.GM29871@nuc-i3427.alporthouse.com> (raw)
In-Reply-To: <7abf8559-3aa7-af3a-8dc1-1dee42019fcd@suse.com>
[-- Attachment #1: Type: text/plain, Size: 1124 bytes --]
On Mon, Dec 19, 2016 at 12:39:16PM +0100, Juergen Gross wrote:
> With recent 4.10 kernel the graphics isn't coming up under Xen. First
> failure message is:
>
> [ 46.656649] i915 0000:00:02.0: swiotlb buffer is full (sz: 1630208 bytes)
Do we get a silent failure? i915_gem_gtt_prepare_pages() is where we
call dma_map_sg() and pass the sg to swiotlb (in this case) for
remapping, and we do check for an error value of 0. After that error,
SWIOTLB_MAP_ERROR is propagated back and converted to 0 for
dma_map_sg(). That looks valid, and we should report ENOMEM back to the
caller.
> Later I see splats like:
>
> [ 49.393583] general protection fault: 0000 [#1] SMP
What was the faulting address? RAX is particularly non-pointer-like so I
wonder if we walked onto an uninitialised portion of the sgtable. We may
have tripped over a bug in our sg_page iterator.
The attached patch should prevent an early ENOMEM following the swiotlb
allocation failure. But I suspect that we will still be tripping up the
failure in the sg walker when binding to the GPU.
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
[-- Attachment #2: 0001-drm-i915-Fallback-to-single-PAGE_SIZE-segments-for-D.patch --]
[-- Type: text/x-diff, Size: 2486 bytes --]
>From e3f9268d467768a31e19d21e2f45e5c9ddd9a0f8 Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Mon, 19 Dec 2016 12:23:43 +0000
Subject: [PATCH] drm/i915: Fallback to single PAGE_SIZE segments for DMA
remapping
If we at first do not succeed with attempting to remap our physical
pages using a coalesced scattergather list, try again with one
scattergather entry per page. This should help with swiotlb as it uses a
limited buffer size and only searches for contiguous chunks within its
buffer aligned up to the next boundary - i.e. we may prematurely cause a
failure as we are unable to utilize the unused space between large
chunks and trigger an error such as:
i915 0000:00:02.0: swiotlb buffer is full (sz: 1630208 bytes)
Reported-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
drivers/gpu/drm/i915/i915_gem.c | 22 ++++++++++++++++++----
1 file changed, 18 insertions(+), 4 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 412f3513f269..509d98887e04 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2326,7 +2326,8 @@ static struct sg_table *
i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
{
struct drm_i915_private *dev_priv = to_i915(obj->base.dev);
- int page_count, i;
+ const unsigned long page_count = obj->base.size / PAGE_SIZE;
+ unsigned long i;
struct address_space *mapping;
struct sg_table *st;
struct scatterlist *sg;
@@ -2352,7 +2353,7 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
if (st == NULL)
return ERR_PTR(-ENOMEM);
- page_count = obj->base.size / PAGE_SIZE;
+rebuild_st:
if (sg_alloc_table(st, page_count, GFP_KERNEL)) {
kfree(st);
return ERR_PTR(-ENOMEM);
@@ -2411,8 +2412,21 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
i915_sg_trim(st);
ret = i915_gem_gtt_prepare_pages(obj, st);
- if (ret)
- goto err_pages;
+ if (ret) {
+ /* DMA remapping failed? One possible cause is that
+ * it could not reserve enough large entries, asking
+ * for PAGE_SIZE chunks may be helpful.
+ */
+ if (max_segment > PAGE_SIZE) {
+ for_each_sgt_page(page, sgt_iter, st)
+ put_page(page);
+ sg_free_table(st);
+
+ max_segment = PAGE_SIZE;
+ goto rebuild_st;
+ } else
+ goto err_pages;
+ }
if (i915_gem_object_needs_bit17_swizzle(obj))
i915_gem_object_do_bit_17_swizzle(obj, st);
--
2.11.0
next prev parent reply other threads:[~2016-12-19 12:29 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-19 11:39 i915 regression in kernel 4.10 Juergen Gross
2016-12-19 12:29 ` Chris Wilson [this message]
2016-12-19 14:16 ` Juergen Gross
2016-12-20 14:42 ` Konrad Rzeszutek Wilk
2016-12-20 16:50 ` Konrad Rzeszutek Wilk
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