On Fri, Aug 07, 2026 at 01:47:34PM -0300, Jason Gunthorpe wrote: > 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: > > > On Fri, Aug 07, 2026 at 02:18:31PM +0100, Will Deacon wrote: > > > > > > > > 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? >
The patches are not in Linux yet, when it eventually lands in Android it should be possible, I did some initial assessment and did not see any regressions. > > 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 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. Thanks, Mostafa > > Jason
