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 48EC53101A0; Tue, 25 Aug 2026 04:42:06 +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=1787632927; cv=none; b=SLqONQ7/nC/SBtqk+hRVmj3oD+iRBL8sVmdCQLmHr+0fevcEi+mwRkfCn0jFULXSsGA1K9m0Lcceh6InuN+xwb3nVUi5skMjChnARTqkFCNBGwmstVHUHairfpxDHxZF9IhgxhKSf/h16VxUw3cE4x3mbV/hQSM4u2Aj0v0iemE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787632927; c=relaxed/simple; bh=XE2Ab0GG9kmt8pSqRAwcSHToJNuqWMlTyG0wNh2OK0k=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=LBJOaejqDuqU4qW8Z1UeZe/Cg7h0Nv2HJgyLNBlFFi8gdKGbFtu3PF1zr24E84KR75gdu6kFqSWmkRRu0J5wKF9w2JYCE9UXdNVyw/7X0zf8MXweiGsq401/9+BUXvLYA4c1jspcV4gItX6TvzXVDMnxnW9cbcSAs9x7IHvFr/o= 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=Q1WplNng; 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="Q1WplNng" Received: from [192.168.1.70] (unknown [4.194.122.170]) by linux.microsoft.com (Postfix) with ESMTPSA id 87D7B20B7166; Mon, 24 Aug 2026 21:41:32 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 87D7B20B7166 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1787632894; bh=2UJlLi20XMSxA7zww1xtzN2KILuXIuj1I5rEPmJqvNE=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Q1WplNng40iw7ncVS17Q5u1PqVWhUxNiymQEfSN2ArTnRFvLIzqzVvrww0xrEqg1H 605U3ofKhG4QG2QZbp5FvZSFQ10JfKF3DhAhyBM/lCbHojurIl9xiwjqRPVpg779RO KCffdDFS9wVMw8jEDoxV6SdBi7lbwZjj4JUZgeh4= Message-ID: Date: Tue, 25 Aug 2026 10:12:01 +0530 Precedence: bulk X-Mailing-List: linux-pci@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/3] PCI: hv: Set irq_retrigger callback for the Hyper-V PCI MSI irqchip To: Wei Liu Cc: sashiko-reviews@lists.linux.dev, linux-pci@vger.kernel.org, linux-hyperv@vger.kernel.org References: <20260728135117.2888175-1-namjain@linux.microsoft.com> <20260728135117.2888175-2-namjain@linux.microsoft.com> <20260728140427.714311F000E9@smtp.kernel.org> <20260824001406.GC3566091@liuwe-devbox-debian-v2.local> <20260824165908.GC3665124@liuwe-devbox-debian-v2.local> Content-Language: en-US From: Naman Jain In-Reply-To: <20260824165908.GC3665124@liuwe-devbox-debian-v2.local> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 8/24/2026 10:29 PM, Wei Liu wrote: > On Mon, Aug 24, 2026 at 11:57:56AM +0530, Naman Jain wrote: >> >> >> On 8/24/2026 5:44 AM, Wei Liu wrote: >>> On Thu, Jul 30, 2026 at 04:56:27PM +0530, Naman Jain wrote: >>>> >>>> >>>> On 7/28/2026 7:34 PM, sashiko-bot@kernel.org wrote: >>>>> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider: >>>>> >>>>> Pre-existing issues: >>>>> - [High] The fix for dropped pending interrupts during CPU hot-unplug was missed in the sister Hyper-V root partition MSI domain. >>>>> -- >>>>> >>>>> --- Patch [1]: [PATCH 1/3] PCI: hv: Set irq_retrigger callback for the Hyper-V PCI MSI irqchip --- >>>>> commit b8b1c843c457dd145f0d360b44f4b1bf34bd8cf5 >>>>> Author: Naman Jain >>>>> >>>>> PCI: hv: Set irq_retrigger callback for the Hyper-V PCI MSI irqchip >>>>> >>>>> The Hyper-V vPCI MSI irqchip never installs an irq_retrigger() callback. >>>>> On CPU hot-unplug fixup_irqs() migrates the interrupts which are affine to >>>>> the outgoing CPU to a new target. As the Hyper-V PCI/MSI chip does not >>>>> provide that callback, the pending interrupt is silently dropped, which >>>>> can result in lost interrupts, stalls and "No irq handler for vector" >>>>> messages. >>>>> >>>>> Fixes: 4daace0d8ce85 ("PCI: hv: Add paravirtual PCI front-end for Microsoft Hyper-V VMs") >>>>> Cc: stable@vger.kernel.org >>>>> Suggested-by: Long Li >>>>> Suggested-by: Thomas Gleixner >>>>> Signed-off-by: Naman Jain >>>>> >>>>>> diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c >>>>>> index cfc8fa403dad6..89816a2bd7cd3 100644 >>>>>> --- a/drivers/pci/controller/pci-hyperv.c >>>>>> +++ b/drivers/pci/controller/pci-hyperv.c >>>>>> @@ -2119,6 +2119,7 @@ static bool hv_pcie_init_dev_msi_info(struct device *dev, struct irq_domain *dom >>>>>> info->ops->msi_prepare = hv_msi_prepare; >>>>>> chip->irq_set_affinity = irq_chip_set_affinity_parent; >>>>>> + chip->irq_retrigger = irq_chip_retrigger_hierarchy; >>>>> >>>>> [Severity: High] >>>>> This isn't a bug introduced by this patch, but does the sister Hyper-V root >>>>> partition MSI domain in arch/x86/hyperv/irqdomain.c also need this fix? >>>>> >>>>> Looking at hv_init_dev_msi_info(), it appears to be missing the exact same >>>>> callback initialization for the root partition's top-level irq_chip: >>>>> >>>>> arch/x86/hyperv/irqdomain.c:hv_init_dev_msi_info() { >>>>> ... >>>>> if (!msi_lib_init_dev_msi_info(dev, domain, real_parent, info)) >>>>> return false; >>>>> >>>>> chip->flags |= IRQCHIP_SKIP_SET_WAKE | IRQCHIP_MOVE_DEFERRED; >>>>> >>>>> info->ops->msi_prepare = pci_msi_prepare; >>>>> >>>>> return true; >>>>> } >>>>> >>>>> If a CPU is hot-unplugged while a device MSI interrupt is pending in its >>>>> local APIC IRR, could fixup_irqs() fail to resend the pending interrupt >>>>> to the new target CPU because this callback is NULL? >>>>> >>>>> This could potentially lead to the same lost interrupts and I/O stalls >>>>> described in this commit message, just in the root partition MSI domain >>>>> instead of the guest paravirtual MSI domain. >>>>> >>>>>> if (IS_ENABLED(CONFIG_X86)) >>>>>> chip->flags |= IRQCHIP_MOVE_DEFERRED; >>>>>> >>>>> >>>> >>>> I am not planning to include this in this series, since this issue is not >>>> seen in root partition yet and I am not sure if it is applicable here. >>>> Second patch would anyways fix it going forward, but I am OK adding the >>>> change for this, if we need. >>> >>> What's the downside of fixing the root partition irq domain? >> >> No downside as such. It would be a latent bug, exposed only if we exercise >> hotplug in root partition, which seems like we don't. After patch 2 of this >> series, that would go away anyways. If you tell me, I can add a change >> similar to patch 1, which is backportable, but then I would need to remove >> it similarly in patch 3. > > Yes, please fix that for the root partition, too. Being consistent > across different use cases is going to save us some headache in the > future. > > Wei Acked. Regards, Naman