# Re: \[PATCH v4 11/15\] pci: Add pci\_iomap\_shared{,\_range} - From: Andi Kleen \ - Date: 2021-08-24 02:14:25 - List: linux-doc - Page: https://ratatoskr.run/linux-doc/2021/08/1486444 - Thread: https://ratatoskr.run/linux-pci/2021/08/1468282/t.md ```text On 8/23/2021 6:04 PM, Dan Williams wrote: > On Mon, Aug 23, 2021 at 5:31 PM Kuppuswamy, Sathyanarayanan > [ref] 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 >>>> Signed-off-by: Kuppuswamy Sathyanarayanan >>> 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. We originally made it default (similar to AMD), but it during code audit we found a lot of drivers who do ioremap early outside the probe function. Since it would be difficult to change them all we made it opt-in, which ensures that only drivers that have been enabled can talk with the host at all and can't be attacked. That made the problem of hardening all these drivers a lot more practical. Currently we only really need virtio and MSI-X shared, so for changing two places in the tree you avoid a lot of headache elsewhere. Note there is still a command line option to override if you want to allow and load other drivers. -Andi ```