Re: [PATCH] mm/filemap: Implement fast short reads

[Yang Shi]

On Thu, Oct 23, 2025 at 3:34 AM Kiryl Shutsemau <kirill@xxxxxxxxxxxxx> wrote:
>
> On Wed, Oct 22, 2025 at 07:28:27PM +0200, David Hildenbrand wrote:
> > "garbage" as in pointing at something without a direct map, something that's
> > protected differently (MTE? weird CoCo protection?) or even worse MMIO with
> > undesired read-effects.
>
> Pedro already points to the problem with missing direct mapping.
> _nofault() copy should help with this.
>
> Can direct mapping ever be converted to MMIO? It can be converted to DMA
> buffer (which is fine), but MMIO? I have not seen it even in virtualized
> environments.
>
> I cannot say for all CoCo protections, but TDX guest shared<->private
> should be fine.
>
> I am not sure about MTE. Is there a way to bypass MTE check for a load?
> And how does it deal with stray reads from load_unaligned_zeropad()?

If I remember correctly, _nofault() copy should skip tag check too.

Thanks,
Yang

>
> --
>   Kiryl Shutsemau / Kirill A. Shutemov
>