On 18.10.2023 13:20, Manuel Bouyer wrote: > On Wed, Oct 18, 2023 at 11:44:22AM +0100, Andrew Cooper wrote: >> On 18/10/2023 11:38 am, Manuel Bouyer wrote: >>> Hello, >>> With Xen 4.18, a PV domain running under pvshim doesn't get console input. >>> This is because the domain id in pvshim isn't 0 (and on x86 max_init_domid >>> is >>> hardwired to 0), so console_input_domain() will never select that domain >>> as input. >>> >>> The attached patch fixes it by translating 0 to the real domain id for >>> pvshim, but there may be a better way to do this. >>> >> >> Thankyou for the report. >> >> First, CC'ing Henry as 4.18 release manager. >> >> There have been changes in how this works recently in 4.18, notably c/s >> c2581c58bec96. > > Yes, it looks like this one introduced the problem. > Before this, we would switch console_rx to 1 without checking if > domain (console_rx - 1) exists, and console_rx == 1 is a special case > in __serial_rx() > >> >> However, it's not obvious whether this worked in 4.17 or not. i.e. >> whether it's a regression in 4.18, or whether it's been broken since PV >> Shim was introduced. > > I don't know for 4.16 or 4.17 but I can tell that it's working in 4.15
>From looking at the code, it doesn't look like it would: There switch_serial_input() toggles console_rx between 0 and 1 afaict, and console_input_domain() handles value 0 as "Xen" (like in 4.18), while otherwise it calls rcu_lock_domain_by_id(console_rx - 1) (i.e. trying to get hold of Dom0's domain structure, not Dom1's). Jan
