On Mon, Aug 23, 2021 at 5:31 PM Kuppuswamy, Sathyanarayanan
[off-list ref] wrote:

On 8/23/21 4:56 PM, Michael S. Tsirkin wrote:

quoted

quoted

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.

That's confusing, isn't device authorization what keeps unaudited
drivers from loading against untrusted devices? I'm feeling like
Michael that this should be a detail that drivers need not care about
explicitly, in which case it does not need to be exported because the
detail can be buried in lower levels.

Note, I specifically said "unaudited", not "hardened" because as Greg
mentioned the kernel must trust drivers, its devices that may not be
trusted.
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