Re: Xorg SEGV in Xen PV dom0 after updating from 5.16.18 to 5.17.5

[Thorsten Leemhuis]

On 04.05.22 08:48, Juergen Gross wrote:
> On 04.05.22 07:46, Thorsten Leemhuis wrote:
>> Hi, this is your Linux kernel regression tracker. Sending this just to
>> CC the developers of the culprit mentioned below (bdd8b6c98239cad
>> ("drm/i915: replace X86_FEATURE_PAT with pat_enabled()")) and the
>> maintainers for the subsystem.
>>
>> While at it a quick note: I wonder if this is problem a similar to one
>> that recently turned up with amdgpu and is fixed by this problem:
>> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=78b12008f20
>>
> 
> No, this is different.
> 
> I have posted a patch yesterday which should fix the issue:
> 
> https://lore.kernel.org/lkml/20220503132207.17234-3-jgross@xxxxxxxx/T/#m75efc68c96d8f7160229b5f3147242221ce0c28c

Ahh, great, thx for letting us know.

#regzbot monitor:
https://lore.kernel.org/lkml/20220503132207.17234-1-jgross@xxxxxxxx/

Ciao, Thorsten

>> Ciao, Thorsten
>>
>> On 04.05.22 02:37, Marek Marczykowski-Górecki wrote:
>>>
>>> After updating from 5.16.18 to 5.17.5 in Xen PV dom0, my Xorg started
>>> crashing when displaying any window mapped from a guest (domU) system.
>>> This is 100% reproducible.
>>> The system is Qubes OS, and it uses a trick that maps windows content
>>> from other guests using Xen grant tables, wrapped as "shared memory"
>>> from Xorg point of view (so, the memory that Xorg mmaps is not just from
>>> another process, but from another VM). That's the ShmPutImage you can
>>> see on the stack trace below.
>>>
>>> Stack trace of thread 12858:
>>> #0  0x00007f80029e17d5 raise (libc.so.6 + 0x3c7d5)
>>> #1  0x00007f80029ca895 abort (libc.so.6 + 0x25895)
>>> #2  0x00005b3469ace0e0 OsAbort (Xorg + 0x1c60e0)
>>> #3  0x00005b3469ad3959 AbortServer (Xorg + 0x1cb959)
>>> #4  0x00005b3469ad46aa FatalError (Xorg + 0x1cc6aa)
>>> #5  0x00005b3469acb450 OsSigHandler (Xorg + 0x1c3450)
>>> #6  0x00007f8002b85a90 __restore_rt (libpthread.so.0 + 0x14a90)
>>> #7  0x00007f8002b0a2a1 __memmove_avx_unaligned_erms (libc.so.6 +
>>> 0x1652a1)
>>> #8  0x00007f80015dfcc9 linear_to_xtiled_faster (iris_dri.so + 0xc91cc9)
>>> #9  0x00007f80015e3477 _isl_memcpy_linear_to_tiled (iris_dri.so +
>>> 0xc95477)
>>> #10 0x00007f8001468440 iris_texture_subdata (iris_dri.so + 0xb1a440)
>>> #11 0x00007f8000a76107 st_TexSubImage (iris_dri.so + 0x128107)
>>> #12 0x00007f8000be9a47 texture_sub_image (iris_dri.so + 0x29ba47)
>>> #13 0x00007f8000becd0c texsubimage_err (iris_dri.so + 0x29ed0c)
>>> #14 0x00007f8000bf2939 _mesa_TexSubImage2D (iris_dri.so + 0x2a4939)
>>> #15 0x00007f800213831f glamor_upload_boxes (libglamoregl.so + 0x1e31f)
>>> #16 0x00007f800213856f glamor_upload_region (libglamoregl.so + 0x1e56f)
>>> #17 0x00007f800212aea6 glamor_put_image (libglamoregl.so + 0x10ea6)
>>> #18 0x00005b3469a4d79c damagePutImage (Xorg + 0x14579c)
>>> #19 0x00005b3469a00a7e ProcShmPutImage (Xorg + 0xf8a7e)
>>> #20 0x00005b3469965a2b Dispatch (Xorg + 0x5da2b)
>>> #21 0x00005b3469969b04 dix_main (Xorg + 0x61b04)
>>> #22 0x00007f80029cc082 __libc_start_main (libc.so.6 + 0x27082)
>>> #23 0x00005b3469952e6e _start (Xorg + 0x4ae6e)
>>>
>>> Disassembly of the surrounding code:
>>>
>>>     0x00007596ae8c82fb <+123>:    ja     0x7596ae8c8338
>>> <__memmove_avx_unaligned_erms+184>
>>>     0x00007596ae8c82fd <+125>:    jb     0x7596ae8c8304
>>> <__memmove_avx_unaligned_erms+132>
>>>     0x00007596ae8c82ff <+127>:    movzbl (%rsi),%ecx
>>>     0x00007596ae8c8302 <+130>:    mov    %cl,(%rdi)
>>>     0x00007596ae8c8304 <+132>:    retq
>>>     0x00007596ae8c8305 <+133>:    vmovdqu (%rsi),%xmm0
>>>     0x00007596ae8c8309 <+137>:    vmovdqu -0x10(%rsi,%rdx,1),%xmm1
>>> => 0x00007596ae8c830f <+143>:    vmovdqu %xmm0,(%rdi)
>>>     0x00007596ae8c8313 <+147>:    vmovdqu %xmm1,-0x10(%rdi,%rdx,1)
>>>     0x00007596ae8c8319 <+153>:    retq
>>>
>>>
>>> I don't see any related kernel or Xen messages at this time. Xorg's SEGV
>>> handler prints also:
>>>
>>>      (EE) Segmentation fault at address 0x3c010
>>>
>>> Git bisect says it's bdd8b6c98239cad ("drm/i915: replace X86_FEATURE_PAT
>>> with pat_enabled()"), and indeed with this commit reverted on top of
>>> 5.17.5 everything works fine.
>>>
>>> I guess this part of dom0's boot dmesg may be relevant:
>>>
>>> [    0.000949] x86/PAT: MTRRs disabled, skipping PAT initialization too.
>>> [    0.000953] x86/PAT: Configuration [0-7]: WB  WT  UC- UC  WC  WP 
>>> UC  UC
>>>
>>> Originally reported at
>>> https://github.com/QubesOS/qubes-issues/issues/7479
>>>
>>>   #regzbot introduced bdd8b6c98239cad
>>> #regzbot monitor: https://github.com/QubesOS/qubes-issues/issues/7479
>>>
>