Re: [PATCH] drm/gem-shmem: Install writable PTEs for write faults

[Thorsten Leemhuis]

On 10/29/26 17:55, Sergio Lopez Pascual wrote:
> Thorsten Leemhuis <regressions@xxxxxxxxxxxxx> writes:
>> [CCing Paolo and Sergio]
>> On 8/4/26 16:57, Konstantin Fastov wrote:
>>> вт, 4 авг. 2026 г. в 17:29, Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>:
>>>> On Tue,  4 Aug 2026 17:04:03 +0300
>>>> Konstantin Fastov <kfastov@xxxxxxxxx> wrote:
>>>>
>>>>> Since the introduction of dirty tracking, drm_gem_shmem_vm_ops has a
>>>>> .pfn_mkwrite handler.  Its presence makes vma_wants_writenotify() true,
>>>>> so vma_set_page_prot() removes the write bit from vm_page_prot of
>>>>> shared mappings, and the vmf_insert_pfn() call in the fault handler now
>>>>> installs read-only PTEs even when serving a write fault.
>>>> [...]
>>>> The same issue is being discussed here [1].
>>>> [...]
>>>> [1]https://lore.kernel.org/dri-devel/20260804120529.1730187-1-pbonzini@xxxxxxxxxx/
> [...]>> FWIW, it seems that series takes a while to get polished and
mainlined:
>> https://lore.kernel.org/all/CABgObfYgZ87%3DW%2B6E%3DN%3DWwTuyYkaoKU3hqd84JDTSAvT3_9dh6w@xxxxxxxxxxxxxx/
>>
>> To quote: "It ballooned a bit and getting acks from everyone involved is
>> hard... Either I or Sergio will get back to it."
>>
>> Is that something you/AsahiLinux/the world can live with?
> 
> Asahi still ships their own kernel with downstream patches, and have
> backported Paolo's series. But for the rest of the world this is pretty
> bad, as it means anything that requires virtio-gpu with blob mappings
> (venus, native context, etc..) is broken.

Thx for this assessment, helped a lot!
> Since the proper fix is going to take a while, I think having some form
> of interim solution could be a good idea.

Sounds like it. Is there one that is in reach? Is reverting the culprit
from Thomas and anything that depends on it an option? Boris patch this
thread is about would not do the trick I assume?

Ciao, Thorsten