Re: Console vs serial

[Frediano Ziglio <frediano.ziglio@xxxxxxxxx>]

On Fri, Aug 1, 2025 at 12:25 PM Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
>
> Hello,
>
> There's a long-standing irritation in Xen, whereby printk()'s which
> occur prior to console_init_preirq() get half-lost.
>
> They end up in the console ring, and hence are available via `xl dmesg`,
> but they're missing from serial console.
>
> e.g. these 4 lines don't escape
>
>     (XEN) Enabling lockdown mode because Secure Boot is enabled
>     (XEN) Lockdown mode is enabled
>     (XEN) Ignoring cmdline option 'hap_2mb' in lockdown mode
>     (XEN) Ignoring cmdline option 'hap_1gb' in lockdown mode
>      __  __            _  _    _  ___   ____
>      \ \/ /___ _ __   | || |  / |/ _ \ |___ \
>
>
> This is from a testcase failure I've just debugged, but the issue is not
> specific to secureboot.  More generally, any diagnostic from cmdline
> parsing ends up in this state.
>
> For PVShim, we did a gross hack to assume the PV console is usable right
> from the outset, but all other console configurations don't start
> working until the cmdline has been parsed.
>
> Is anything stopping us from feeding the current contents of the console
> ring into serial in console_init_preirq()?
>
> ~Andrew
>

I don't think there's a problem replaying the console logs into the
serial once the serial is set up.
It will slow down the boot maybe but beside that it should be fine.

Frediano