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

[Marek Marczykowski <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

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.

> >> Andrew suggested to move set_irq_regs() to BUGFRAME_run_fn handling;
> >> it's not clear to me whether that would be (a) correct from an abstract
> >> pov (that's exception, not interrupt context after all) 
> > 
> > I agree with that.
> > 
> >> and (b) really beneficial.
> > 
> > I guess this could help to reduce the amount of churn. I can't really 
> > make my mind whether this is worth it or not. So I would keep it as you did.
> 
> Good, thanks.
> 
> Jan

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

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