Re: [PATCH v3 1/8] serial: fake IRQ-regs context in poll handlers

[Marek Marczykowski <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

On Tue, Feb 13, 2024 at 08:45:54AM +0100, Jan Beulich wrote:
> On 13.02.2024 04:43, Marek Marczykowski wrote:
> > On Mon, Feb 12, 2024 at 10:04:38AM +0100, Jan Beulich wrote:
> >> On 08.02.2024 23:00, Julien Grall wrote:
> >>> On 05/02/2024 13:27, Jan Beulich wrote:
> >>>> In preparation of dropping the register parameters from
> >>>> serial_[rt]x_interrupt() and in turn from IRQ handler functions,
> >>>> register state needs making available another way for the few key
> >>>> handlers which need it. Fake IRQ-like state.
> >>>>
> >>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> >>>> ---
> >>>> The use of guest_cpu_user_regs() in dbc_uart_poll() is inconsistent with
> >>>> other console poll functions we have, and it's unclear whether that's
> >>>> actually generally correct.
> >>>
> >>> Is it? Looking at ns16550_poll() we would pass guest_user_regs() if 
> >>> run_in_exception() doesn't exist. But looking at the caller, no-on seems 
> >>> to care about the 'regs'. So is this just a latent bug?
> >>
> >> What do you mean by "doesn't exist"? ns16550_poll() assumes it exists.
> >> And I can spot any use of guest_user_regs() on the respective generic
> >> or Arm-specific bug.c paths.
> >>
> >>> BTW, do you have an idea why the poll function is not run in an 
> >>> exception handler?
> >>
> >> "The poll function" being which one? If you mean the one in xhci-dbc.c
> >> then that's why I had Cc-ed Marek. Moving him to To: - maybe that
> >> manages to finally catch his attention.
> > 
> > TBH, I don't know. That's part of the original xue patch at
> > https://github.com/connojd/xue/blob/master/patches/xen-xue-dbgp.patch
> > and it works for me as it is.
> 
> "Works" meaning what? Doesn't crash on you? Or does also provide
> sensible output in _all_ cases (i.e. including when e.g. the poll
> happens to run on an idle vCPU)?

Generally provides sensible output, for example during boot (it is using
idle vCPU then, right?).

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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