Re: [PATCH dovetail] irq_pipeline: synchronize inband IRQ log in exit_to_user_mode_prepare()

On Mon, 2026-02-16 at 15:30 +0100, Philippe Gerum wrote:
> Florian Bezdeka <[email protected]> writes:
> 
> > On 2/14/26 12:39, Tobias Schaffner wrote:
> > > Architectures using the generic handle_irq_pipelined() path do not
> > 
> > arm64 and x86 are not using that, so the only arch left is arm.
> > See below...
> > 
> > > synchronize the inband IRQ log in handle_irq_pipelined_finish()
> > > because inband is still stalled from irqentry_enter() when it gets
> > > called.
> > 
> > I think the real issue / correct wording is:
> > 
> > _TIF_WORK is left pending on IRQ exit.
> > 
> 
> More precisely, some IRQs might be logged for the in-band stage (taken
> during stage demotion but virtually masked, as your pointed out), and we
> must play them before returning to userland.
> 
> [snip]
> 
> > Taken from arm64/x86:
> > if (unlikely(running_oob() || irqs_disabled())) {
> > 	...
> > 	handle_irq_pipelined_finish(prevd, regs);
> > 	if (running_inband() && user_mode(regs)) {
> > 		stall_inband_nocheck();
> > 		irqentry_exit_to_user_mode(regs);
> > 	}
> > 	...
> > }
> > 
> > >  again:
> > >  	ti_work = read_thread_flags();
> > >  	if (unlikely(ti_work & EXIT_TO_USER_MODE_WORK))
> 
> Incidentally, I just noticed that arm64 looks wrong
> here. arm64_pipeline_el0_irq() lacks the demotion check in the
> running_oob() case, and arm64_pipeline_el1_irq() unfortunately checks
> for user_mode(regs) in arm64_pipeline_el1_irq(). I'll leave the
> conclusion to the careful reader.

I noticed that as well while reviewing the patch proposal from Tobias.
Patch is already under CI testing...


> 
> > 
> > That said, we should double check that this corner case is handled right
> > on arm. If arm suffers from the same problem, this corner case is
> > missing in handle_irq_pipelined().
> > 
> > I hope all of this makes sense at the end. It's late...
> > 
> > Best regards,
> > Florian
> > 
> > [2. text/vcard; florian_bezdeka.vcf]...
> 
> -- 
> Philippe.