Bug 110602

Summary:	i965 miptree MCS aux_buf allocation failure with old kernels
Product:	Mesa	Reporter:	Anssi Hannula <anssi.hannula>
Component:	Drivers/DRI/i965	Assignee:	Intel 3D Bugs Mailing List <intel-3d-bugs>
Status:	RESOLVED MOVED	QA Contact:	Intel 3D Bugs Mailing List <intel-3d-bugs>
Severity:	normal
Priority:	medium	CC:	nanleychery
Version:	git
Hardware:	All
OS:	Linux (All)
Whiteboard:
i915 platform:		i915 features:
Attachments:	glxinfo Add MMAP_WC check before using MCS Testcase Qt C++ program Testcase apitrace Fallback to non-raw mapping

Description Anssi Hannula 2019-05-03 14:17:03 UTC

Created attachment 144147 [details]
glxinfo

intel_miptree_choose_aux_usage() selects ISL_AUX_USAGE_MCS if intel_miptree_supports_mcs() returns true.

This will cause callchain intel_miptree_alloc_aux() => intel_alloc_aux_buffer() => brw_bo_map(x,y,MAP_RAW|MAP_WRITE) => brw_bo_map_wc(), which checks bufmgr->has_mmap_wc and returns NULL on !bufmgr->has_mmap_wc. There is no fallback in brw_bo_map() for the MAP_RAW case.

This will cause intel_miptree_create() to fail which causes intel_miptree_create_for_renderbuffer() to fail.

I guess either either the miptree creation should be retried without MCS or intel_miptree_supports_mcs() should detect the missing mmap_wc support and return false.

Attached is a quick hack patch that adds mmap_wc check in intel_miptree_supports_mcs(), and it seems to fix the testcase I used (mesa-issue-qt3d.cc).
Without the patch the testcase either crashes (git master) or flashes rapidly (git master + two patches from bug #110601 to workaround the crashes).

The testcase mesa-issue-qt3d.cc is also attached, plus an apitrace and glxinfo with git master.

This was tested on a ValleyView Gen7 (8086:0f31) with kernel 3.10.35.

Comment 1 Anssi Hannula 2019-05-03 14:17:55 UTC

Created attachment 144148 [details] [review]
Add MMAP_WC check before using MCS

Comment 2 Anssi Hannula 2019-05-03 14:18:12 UTC

Created attachment 144149 [details]
Testcase Qt C++ program

Comment 3 Anssi Hannula 2019-05-03 14:18:29 UTC

Created attachment 144150 [details]
Testcase apitrace

Comment 4 Nanley Chery 2019-05-03 14:44:56 UTC

Hi Anssi,

I actually have a series that allows the GL drivers to fallback to not having compression if auxiliary surface allocation fails. Does this branch fix your issue? https://gitlab.freedesktop.org/nchery/mesa/tree/sent/refactor/aux-assign

Comment 5 Anssi Hannula 2019-05-03 15:15:18 UTC

Yes, it indeed does fix this bug, thanks.

Comment 6 Nanley Chery 2019-05-03 16:14:16 UTC

An better performing fix (and possibly the right fix) would involve falling back to a supported mapping. Though, I'm not sure if there would be anything blocking that solution.

Comment 7 Kenneth Graunke 2019-05-03 16:46:11 UTC

I think we can drop MAP_RAW if MMAP_WC isn't supported - using a tiled mapping is kind of weird, but we're just filling the whole buffer anyway.  We used to do it before 3b4f432d9bbdf86bb6e0e84c6053959aa3194daa.

Comment 8 Anssi Hannula 2019-05-06 08:42:29 UTC

Created attachment 144171 [details] [review]
Fallback to non-raw mapping

Indeed, the attached patch that simply fallbacks to non-MAP_RAW seems to also work, at least with my testcase.

The patch fallbacks to non-raw in all cases, no idea if that is wanted or just for MCS.

Comment 9 GitLab Migration User 2019-09-25 20:33:17 UTC

-- GitLab Migration Automatic Message --

This bug has been migrated to freedesktop.org's GitLab instance and has been closed from further activity.

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