From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by smtp.subspace.kernel.org (Postfix) with ESMTP id D81173101D8; Fri, 6 Feb 2026 07:33:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=13.77.154.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770363183; cv=none; b=shhgPlrDxq7B11vNN8vVgBxDzSKY81VA/i11dvuvmiJacCfyiG77hDG02S/Lh3GkxeayQajyjoUETU5J05qH2svxpuKmT+I3QfYiu/PcaAnODY5yDJ4dgC0AYtTCJE9CHn3w7Ddey9wHe6h1fLl65YVBVInXwBRp1/RUAuv8n7I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770363183; c=relaxed/simple; bh=OZRRqQ9EfucDYWsTtIOflSfSOiOC3B974b6H7plpHp0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=J6T18eQtWTPpOvbaTWA+QvOhxrobT5yNJHaDP2RdU6bJOITxzTysxv+A6wlyMb9hDwa3ZrHsk7UgJqETE1vReT4KyL+HprA5gsjydo9pUJK1n1lDhnAZOd4Kz9iqNknQT4aSW94orbd1+gEp/OoUNHpQZ8p18thnzFFfVI2CUh4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com; spf=pass smtp.mailfrom=linux.microsoft.com; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b=CfqSoJ8U; arc=none smtp.client-ip=13.77.154.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b="CfqSoJ8U" Received: from [100.67.96.222] (unknown [52.163.67.188]) by linux.microsoft.com (Postfix) with ESMTPSA id 732E320B7168; Thu, 5 Feb 2026 23:32:56 -0800 (PST) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 732E320B7168 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1770363182; bh=4SGW3YwPxqqxGNqC6P5CHOeKcEhWll027SxxiPevSCg=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=CfqSoJ8Us5fyp1MXEtz+C3vKmqhfx1xBtqX8Du9o8s97zRRLrkC+vWQM7u+H/e+Zw PazFbzE74YL5W7fjqVw7ZYK9ADJZd7coItbgjRv6VYjUzQ3M2nkM5MxaxE13SqcnZr EdWp70ubTgIF+0MNyAtW5oyAYZhgTcnvKZWXIzYg= Message-ID: <76e8cfd8-f48d-4129-bb9d-ca58c24b29a4@linux.microsoft.com> Date: Fri, 6 Feb 2026 13:02:52 +0530 Precedence: bulk X-Mailing-List: linux-rt-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] x86: mshyperv: Use kthread for vmbus interrupts on PREEMPT_RT To: Wei Liu , Jan Kiszka Cc: Magnus Kulke , "K. Y. Srinivasan" , Haiyang Zhang , Dexuan Cui , Long Li , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org, Florian Bezdeka , RT , Mitchell Levy , skinsburskii@linux.microsoft.com, mrathor@linux.microsoft.com, anirudh@anirudhrb.com, schakrabarti@linux.microsoft.com, ssengar@linux.microsoft.com References: <133a95d9-8148-40ea-9acc-edfd8e3ceef4@siemens.com> <20260204070004.GM79272@liuwe-devbox-debian-v2.local> <10ec70f2-27a5-477f-b6e9-164f7b7545d9@siemens.com> <20260204072930.GO79272@liuwe-devbox-debian-v2.local> <20260204073629.GP79272@liuwe-devbox-debian-v2.local> Content-Language: en-US From: Naman Jain In-Reply-To: <20260204073629.GP79272@liuwe-devbox-debian-v2.local> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2/4/2026 1:06 PM, Wei Liu wrote: > On Wed, Feb 04, 2026 at 08:32:04AM +0100, Jan Kiszka wrote: >> On 04.02.26 08:29, Wei Liu wrote: >>> 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 >>>>>>> >>>>>>> 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. >>> >> >> But if my VM is not a root partition, I wouldn't use that driver, would I? > > No, you wouldn't. You cannot do that until later this year. If you > cannot test that, so be it. I'm fine with applying your patch and then > move the mshv_handler logic later ourselves. > > I've CC'ed a few folks from Microsoft. > > Saurabh, Long, and Dexuan, can you review and test this patch for VMBus? I tested this and didn't see any issues with OpenHCL/mshv_vtl. Regards, Naman