[Xen-devel] Upstream Dom0 DRM problems regarding swiotlb

[Michael Labriola <michael.d.labriola@xxxxxxxxx>]

Konrad,

Starting w/ v4.17, I cannot log in to GNOME w/out getting the
following mess in dmesg and ending up back at the GDM login screen.

[   28.554259] radeon_dp_aux_transfer_native: 200 callbacks suppressed
[   31.219821] radeon 0000:01:00.0: swiotlb buffer is full (sz: 2097152 bytes)
[   31.220030] [drm:radeon_gem_object_create [radeon]] *ERROR* Failed
to allocate GEM object (16384000, 2, 4096, -14)
[   31.226109] radeon 0000:01:00.0: swiotlb buffer is full (sz: 2097152 bytes)
[   31.226300] [drm:radeon_gem_object_create [radeon]] *ERROR* Failed
to allocate GEM object (16384000, 2, 4096, -14)
[   31.300734] gnome-shell[1935]: segfault at 88 ip 00007f39151cd904
sp 00007ffc97611ad8 error 4 in libmutter-cogl.so[7f3915178000+aa000]
[   31.300745] Code: 5f c3 0f 1f 40 00 48 8b 47 78 48 8b 40 40 ff e0
66 0f 1f 44 00 00 48 8b 47 78 48 8b 40 48 ff e0 66 0f 1f 44 00 00 48
8b 47 78 <48> 8b 80 88 00 00 00 ff e0 0f 1f 00 48 8b 47 78 48 8b 40 68
ff e0
[   38.193302] radeon_dp_aux_transfer_native: 116 callbacks suppressed
[   40.009317] radeon 0000:01:00.0: swiotlb buffer is full (sz: 2097152 bytes)
[   40.009488] [drm:radeon_gem_object_create [radeon]] *ERROR* Failed
to allocate GEM object (16384000, 2, 4096, -14)
[   40.015114] radeon 0000:01:00.0: swiotlb buffer is full (sz: 2097152 bytes)
[   40.015297] [drm:radeon_gem_object_create [radeon]] *ERROR* Failed
to allocate GEM object (16384000, 2, 4096, -14)
[   40.028302] gnome-shell[2431]: segfault at 2dadf40 ip
0000000002dadf40 sp 00007ffcd24ea5f8 error 15
[   40.028306] Code: 20 6e 31 00 00 00 00 00 00 00 00 37 e3 3d 2d 7f
00 00 80 f4 e6 3d 2d 7f 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 <00> 00 00 00 00 00 00 00 c1 00 00 00 00 00 00 00 80 e1 d2 03
00 00


This happens w/ both radeon and amdgpu.

I bisected down to the following range of commits, which basically add
conditional code to radeon and amdgpu to NOT use swiotlb if dma_bits
is smaller than the system's max iomem address...  but that very much
doesn't work on a Xen dom0.

82626363 drm: add func to get max iomem address v2
fd5fd480 drm/amdgpu: only enable swiotlb alloc when need v2
1bc3d3cc drm/radeon: only enable swiotlb path when need v2

Reverting the offending commits gives me a usable v4.20 dom0 kernel w/
working 3d support.  Not sure what the appropriate upstream fix for
this would be, as I don't 100% understand this.  Could you enlighten
me?  ;-)

FYI, this is on an x86_64 CentOS 7 machine w/ Xen 4.11.1 (installed by
me, from source).

Thanks!

-Mike

-- 
Michael D Labriola
21 Rip Van Winkle Cir
Warwick, RI 02886
401-316-9844 (cell)
401-848-8871 (work)
401-234-1306 (home)

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