Re: [PATCH v4 04/13] dma: swiotlb: track pool encryption state and honor DMA_ATTR_CC_SHARED

On Tue, May 19, 2026 at 11:06:52AM +0000, Mostafa Saleh wrote:

quoted

quoted

One other interesting case for device-passthrough is non-coherent
devices which then require private pools for bouncing.

Why does shared/private matter for bouncing? Why do you need to bounce
at all? Do cmo's not work in pkvm guests?

At the moment, in iommu_dma_map_phys(), if a non coherent device
tries to map an unaligned address or size it will be bounced.

Sure, that's fine.

In pKVM, dma-iommu is used for assigned devices which operate on
private memory, so bouncing that through the SWIOTLB would leak
information from the guest as the SWIOTLB is decrypted.

Yes, a device that can do private access should not be using a shared
SWIOTLB, that should be part of the selection logic inside the SWIOTLB
stuff..

Jason