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

On Fri, Aug 07, 2026 at 03:34:47PM +0000, Mostafa Saleh wrote:

On Fri, Aug 07, 2026 at 10:58:10AM -0300, Jason Gunthorpe wrote:

quoted

On Fri, Aug 07, 2026 at 02:18:31PM +0100, Will Deacon wrote:

quoted

quoted

I was under the impression that there is a possibility of using swiotlb
instead of restricted-dma-pool with pKVM.

Yes, that patch enables swiotlb as a possibility for protected guests
but with your patch we avoid shrinking the swiotlb buffer even when
restricted dma pools are being used and that's a waste of memory.

I also thought we switched pkvm to use CC-like swiotlb as part of the
alignment in this rework? Mostafa ?

Yes, now protected VMs can use the SWIOTLB for bouncing. However for
Android (and kvmtool), use restricted DMA. so SWIOTLB is not used.

Oh? Why?

However, I do not think we should over engineer this in the code,
swiotlb can be set from the cmdline and now through Kconfig also.

That's fine for android, but real users buying a cloud VM and sticking
a distro on it shouldn't be expected to have to mess with cmdline just
go get a halfway working system

Jason