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

On 07.08.2026 20:20, Jason Gunthorpe wrote:

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?

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