Re: [PATCH v3 3/4] fbdev/deferred-io: Support contiguous kernel memory framebuffers

Thomas Zimmermann
2025-06-03T06:25:33Z

Hi

Am 03.06.25 um 03:49 schrieb Michael Kelley:
[...]
>> Will the VMA have VM_PFNMAP or VM_MIXEDMAP set? PFN_SPECIAL is a
>> horrible hack.
>>
>> In another thread, you mention that you use PFN_SPECIAL to bypass the
>> check in vm_mixed_ok(), so VM_MIXEDMAP is likely not set?
> The VMA has VM_PFNMAP set, not VM_MIXEDMAP. It seemed like
> VM_MIXEDMAP is somewhat of a superset of VM_PFNMAP, but maybe that's
> a wrong impression. vm_mixed_ok() does a thorough job of validating the
> use of __vm_insert_mixed(), and since what I did was allowed, I thought
> perhaps it was OK. Your feedback has set me straight, and that's what I
> needed. :-)
>
> But the whole approach is moot with Alistair Popple's patch set that
> eliminates pfn_t. Is there an existing mm API that will do mkwrite on a
> special PTE in a VM_PFNMAP VMA? I didn't see one, but maybe I missed
> it. If there's not one, I'll take a crack at adding it in the next version of my
> patch set.

What is the motivation behind this work? The driver or fbdev as a whole
does not have much of a future anyway.

I'd like to suggest removing hyperv_fb entirely in favor of hypervdrm?

Best regards
Thomas

>
> Michael

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Thomas Zimmermann
Graphics Driver Developer
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