# Re: \[PATCH v4 11/15\] pci: Add pci\_iomap\_shared{,\_range}

- From: Michael S. Tsirkin \<mst@redhat.com\>
- Date: 2021-08-24 09:12:17 
- List: linux-doc
- Page: https://ratatoskr.run/linux-doc/2021/08/1486765
- Thread: https://ratatoskr.run/linux-pci/2021/08/1468282/t.md

```text
On Mon, Aug 23, 2021 at 05:30:54PM -0700, Kuppuswamy, Sathyanarayanan wrote:
> 
> 
> On 8/23/21 4:56 PM, Michael S. Tsirkin wrote:
> > > Add a new variant of pci_iomap for mapping all PCI resources
> > > of a devices as shared memory with a hypervisor in a confidential
> > > guest.
> > > 
> > > Signed-off-by: Andi Kleen<redacted>
> > > Signed-off-by: Kuppuswamy Sathyanarayanan<sathyanarayanan.kuppuswamy@linux.intel.com>
> > I'm a bit puzzled by this part. So why should the guest*not*  map
> > pci memory as shared? And if the answer is never (as it seems to be)
> > then why not just make regular pci_iomap DTRT?
> 
> It is in the context of confidential guest (where VMM is un-trusted). So
> we don't want to make all PCI resource as shared. It should be allowed
> only for hardened drivers/devices.

I can't say this answers the question at all. PCI devices are part of
the VMM and so un-trusted. In particular PCI devices do not have
the key to decrypt memory. Therefore as far as I can see PCI resources
should not be encrypted.  I conclude they all should be marked
shared.

If I'm wrong can you please give an example of a PCI resource
that is encrypted?

-- 
MST

```