On Fri, Oct 23, 2026 at 01:27:15PM -0500, Bjorn Helgaas wrote: > > Yes, the ACS combination is selected to avoid ordering issues > > Does a user have any way to know whether the configuration is safe?
No, unfortunately in PCIe so much is really difficult when it comes to deployment :( > I'm wondering whether users might use "pci=config_acs=" to configure > ACS so things appear to work as they prefer but may not provide the > ordering guarantees drivers depend on. I imagine that could happen, but on most practical systems the root complex will blow up if you do asymmetric routing so there is an early indication. I know this because I've help debug such configurations at customers. Some servers helpfully MCE if you do this. Lovely. > If that's a possibility, do we have any notes in dmesg that we are > depending on fabric behavior that the OS can't discover and verify? Maybe, it could be interesting if the P2P logic found asymetric paths it refuses to permit it. Jason
