Re: [PATCH] x86: mshyperv: Use kthread for vmbus interrupts on PREEMPT_RT

[Wei Liu <wei.liu@kernel.org>]

On Wed, Feb 04, 2026 at 08:26:48AM +0100, Jan Kiszka wrote:
> On 04.02.26 08:19, Jan Kiszka wrote:
> > On 04.02.26 08:00, Wei Liu wrote:
> >> On Tue, Feb 03, 2026 at 05:01:30PM +0100, Jan Kiszka wrote:
> >>> From: Jan Kiszka <jan.kiszka@siemens.com>
> >>>
> >>> Resolves the following lockdep report when booting PREEMPT_RT on Hyper-V
> >>> with related guest support enabled:
> >>
> >> So all it takes to reproduce this is to enabled PREEMPT_RT?
> >>
> > 
> > ...and enable CONFIG_PROVE_LOCKING so that you do not have to wait for
> > your system to actually run into the bug. Lockdep already triggers
> > during bootup.
> > 
> >> Asking because ...
> >>
> >>>  	struct pt_regs *old_regs = set_irq_regs(regs);
> >>> @@ -158,8 +196,12 @@ DEFINE_IDTENTRY_SYSVEC(sysvec_hyperv_callback)
> >>>  	if (mshv_handler)
> >>>  		mshv_handler();
> >>
> >> ... to err on the safe side we should probably do the same for
> >> mshv_handler as well.
> >>
> > 
> > Valid question. We so far worked based on lockdep reports, and the
> > mshv_handler didn't trigger yet. Either it is not run in our setup, or
> > it is actually already fine. But I have a code review on my agenda
> > regarding potential remaining issues in mshv.
> > 
> > Is there something needed to trigger the mshv_handler so that we can
> > test it?
> > 
> 
> Ah, that depends on CONFIG_MSHV_ROOT. Is that related to the accelerator
> mode that Magnus presented in [1]? We briefly chatted about it and also
> my problems with the drivers after his talk on Saturday.

Yes. That is the driver. If PROVE_LOCKING triggers the warning without
running the code, perhaps turning on MSHV_ROOT is enough.

Wei

> 
> Jan
> 
> [1]
> https://fosdem.org/2026/schedule/event/BFQ8XA-introducing-mshv-accelerator-in-qemu/
> 
> -- 
> Siemens AG, Foundational Technologies
> Linux Expert Center
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