Re: [PATCH 0/2] Add larger page size support for USB audio offload path

[Michal Pecio]

Hi,

On Mon, 24 Aug 2026 19:06:54 -0700, Wesley Cheng wrote:
> On some environments, 16kB pages can be enabled from the Linux subsystem,
> which manages the IOMMU mappings for the audio DSP within the system.  In
> the current design, the following assumptions break when 16k pages are
> utilized:
>   1. xHCI ring size is equal to PAGE_SIZE
>   2. Ring addresses start at the beginning of a page

FYI it's worse than you think - xhci_ring_to_sgtable() returns wrong
data and uses some allocation out of bounds on these systems. Quickly
scanning through the patch I haven't noticed any changes there.

> When the USB offload driver maps the rings (w/ the audio DSP SID), it is
> set with a 16k granular, which is a problem, as several xHCI rings could
> exist on the same page.  This is because the rings are currently allocated
> from the segment_pool.  Hence, potentially mapping non USB audio related
> rings into the region accessible by the audio DSP.

If that's a security or reliability concern, perhaps each sideband
instance should create its own DMA pool, as opposed to allocating every
ring segment on a separate page?

I suppose each 'xhci_ring' could keep a pointer to its segment pool and
things would work for everyone, with very few changes.

Regards,
Michal