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. 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. Thanks, Mostafa > > > > If that is not the case, then we could change: > > > > > > !cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT) && > > > > > > to > > > > > > !is_realm_world() && > > > > Perhaps, or you could just pass the swiotlb= option if the defaults don't > > work for you. Can you give more details about the slots exhaustion you're > > seeing under CCA? > > We see badness with swiotlb too, it basically doesn't work out of the > box if you have to use it 100% for real devices. It easily runs out > of memory. > > Auto tuning to higher levels makes sense to me, but I'd rather the > core code handled adjusting its size to the estimated need, not arch > code. > > Jason
