Re: [PATCH] arm64: swiotlb: Keep the default size for protected guests

On 10.08.2026 12:20, Will Deacon wrote:

On Mon, Aug 10, 2026 at 02:59:42PM +0530, Aneesh Kumar K.V wrote:

quoted

Marek Szyprowski [off-list ref] writes:

quoted

On 07.08.2026 20:20, Jason Gunthorpe wrote:

quoted

On Fri, Aug 07, 2026 at 06:13:49PM +0000, Mostafa Saleh wrote:

quoted

But the whole thing is best effort anyway, the kernel picks
IO_TLB_DEFAULT_SIZE which does not depend on the system topology or
how many devices or how much DMA they do.
SWIOTLB memory is wasted if unused so we should be careful around
that as it would be the other way around and users would have to
decrease it manually.

Yeah, it is why the arch code shouldn't really be sizing it directly,
it should be done in common code and, yes, we are probably going to
have to do something alot smarter to have the common code better
auto-tune this for the CC case..

What about the $subject patch? I assume that it is still needed to

restore the behavior that was altered by the "[PATCH v8 00/23]

dma-mapping: Track shared DMA state through direct, pool and swiotlb

paths?" patchset?

I would request that we pick this patch to fix the regression described
in https://lore.kernel.org/all/yq5azeyxyfol.fsf@kernel.org/ (local).

I really don't think we need it. CCA hardware isn't exactly widespread
and the KVM host side patches don't appear close to being merged.

Does this mean that the branch for-next/coco [1] won't go to v7.3-rc1?

I've used it as a base for the mentioned DMA-mapping patchset.


[1] https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/log/?h=for-next/coco

We have time to fix this properly, rather than papering over it in the
arch code.

Please consider this a NAK from the arm64 side on this patch.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland