linux-kernel - Re: [PATCH] x86: mshyperv: Use kthread for vmbus interrupts on PREEMPT

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20260204072930.GO79272@liuwe-devbox-debian-v2.local>
Date: Wed, 4 Feb 2026 07:29:30 +0000
From: Wei Liu <wei.liu@...nel.org>
To: Jan Kiszka <jan.kiszka@...mens.com>
Cc: Wei Liu <wei.liu@...nel.org>,
	Magnus Kulke <magnuskulke@...ux.microsoft.com>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Dexuan Cui <decui@...rosoft.com>, Long Li <longli@...rosoft.com>,
	Thomas Gleixner <tglx@...nel.org>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
	Florian Bezdeka <florian.bezdeka@...mens.com>,
	RT <linux-rt-users@...r.kernel.org>,
	Mitchell Levy <levymitchell0@...il.com>
Subject: Re: [PATCH] x86: mshyperv: Use kthread for vmbus interrupts on
 PREEMPT_RT

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@...mens.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
>