Re: [PATCH 1/2] xen/swiotlb: relax alignment requirements

[Jürgen Groß]

On 12.02.25 07:53, Jan Beulich wrote:
> On 11.02.2025 13:04, Juergen Gross wrote:
> > When mapping a buffer for DMA via .map_page or .map_sg DMA operations,
> > there is no need to check the machine frames to be aligned according
> > to the mapped areas size. All what is needed in these cases is that the
> > buffer is contiguous at machine level.
>
> Is this really true in all cases? Can't e.g. compound pages make it here,
> with the caller then still being permitted to assume higher than page
> alignment? Alignment checking in xen_swiotlb_map_page() would perhaps
> need doing with the base address of the incoming page, i.e. excluding
> the incoming offset.

The DMA interfaces in question (.map_page and .map_sg) are explicitly
designed for DMA streaming mode. I don't think streaming mode requires a
special page alignment.


Juergen

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