Re: [XEN][PATCH] console/consoleio: account for xen serial input focus during write

[Grygorii Strashko <grygorii_strashko@xxxxxxxx>]

On 05.12.25 09:39, Jan Beulich wrote:
> On 05.12.2025 00:32, Grygorii Strashko wrote:
> > From: Grygorii Strashko <grygorii_strashko@xxxxxxxx>
> >
> > When 2 or more domains are created and:
> > - one is hwdom with "hvc0" (console_io) console
> > - other DomUs with vpl011 or "hvc0" (console_io) console
> > console output from hwdom may mix with output from other domains.
> >
> > Example:
> > [    2.288816] Key type id_legacy registered
> > [    2.291894] n(XEN) DOM1: [    1.016950] DMA: preallocated 128 KiB 
> > GFP_KERNEL|GFP_DMA32 pool for atomic allocations
> > fs4filelayout_init: NFSv4 File Layout Driver Registering...
> > (XEN) DOM1: [    1.018846] audit: initializing netlink subsys (disabled)
> >
> > This happens because for hwdom the console output is produced by domain and
> > handled by Xen as stream of chars, which can be interrupted when hwdom is
> > scheduled out and so, cause console output mix.
> > The Xen consoleio code trying to mimic serial HW behavior for hwdom
> > unconditionally by sending available data to serial HW on arrival.
> > Xen consoleio code does not account for Xen console input focus, comparing
> > to emulated serial hw, like vpl011, which does the same for domain with
> > active Xen console input focus only.
> >
> > Switching console input focus to Xen improves situation, but not enough.
> >
> > This patch changes consoleio code to account for domain with active Xen
> > console input focus - console output will be sent directly to serial HW
> > only if domain has active Xen console input focus. For other domains -
> > console output will be buffered and sync on per-line basis.
> >
> > Example output:
> > (d2) [    4.263417] Key type id_legacy registered
> > (XEN) DOM1: [    4.658080] Advanced Linux Sound Architecture Driver Initialized.
> > (d2) [    4.277824] nfs4filelayout_init: NFSv4 File Layout Driver Registering...
> >
> > Signed-off-by: Grygorii Strashko <grygorii_strashko@xxxxxxxx>
> > ---
> > This causes random multi-domain tests failures due to inter-domain console
> > mixing which breaks console parsing checks.
> This remark reads as if "here's a patch, but it breaks things". Instead of
> merely "This", did you maybe mean "The original behavior" or some such?
Right.

"
The original behavior causes random multi-domain tests failures due to 
inter-domain console
mixing which breaks console parsing checks.
"

--
Best regards,
-grygorii