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

[Jason Gunthorpe <jgg@ziepe.ca>]

On Tue, May 19, 2026 at 01:41:42PM +0000, Mostafa Saleh wrote:
> On Tue, May 19, 2026 at 10:29:11AM -0300, Jason Gunthorpe wrote:
> > On Tue, May 19, 2026 at 11:04:37AM +0000, Mostafa Saleh wrote:
> > > On Thu, May 14, 2026 at 08:13:25PM +0530, Aneesh Kumar K.V wrote:
> > > > >> 
> > > > >> What I meant was that we need a generic way to identify a pKVM guest, so
> > > > >> that we can use it in the conditional above.
> > > > >
> > > > > I have this patch, with that I can boot with your series unmodified,
> > > > > but I will need to do more testing.
> > > > >
> > > > 
> > > > Thanks, I can add this to the series once you complete the required testing.
> > > > 
> > > 
> > > I am still running more tests, but looking more into it. Setting
> > > force_dma_unencrypted() to true for pKVM guests is wrong, as the
> > > guest shouldn’t try to decrypt arbitrary memory as it can include
> > > sensitive information (for example in case of virtio sub-page
> > > allocation) and should strictly rely on the restricted-dma-pool
> > > for that.
> > 
> > ??
> > 
> > Where does force_dma_unencrypted() cause arbitary memory passed into
> > the DMA API to be decrypted? That should never happen???
> 
> Sorry, maybe arbitrary is not the right expression again :)
> I mean that, with emulated devices that use the DMA-API under pKVM,
> they will map memory coming from other layers (VFS, net) through
> vitrio-block, virtio-net... These can be smaller than a page, and
> using force_dma_unencrypted() will share the whole page.

force_dma_unencrypted() should only trigger swiotlb and that never
memcpy's more than necessary?

Where does it do otherwise? That sounds like a bug?

Jason