linux-kernel - Re: [PATCH 6.6 and older] uio_hv_generic: Enable user space to manage interrupt

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Message-ID: <2025112109-legroom-resend-643f@gregkh>
Date: Fri, 21 Nov 2025 11:10:43 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Naman Jain <namjain@...ux.microsoft.com>
Cc: Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
	Michael Kelley <mhklinux@...look.com>,
	Long Li <longli@...rosoft.com>,
	Saurabh Sengar <ssengar@...ux.microsoft.com>,
	"K . Y . Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Tianyu Lan <tiala@...rosoft.com>, linux-hyperv@...r.kernel.org,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	Salvatore Bonaccorso <carnil@...ian.org>,
	Peter Morrow <pdmorrow@...il.com>
Subject: Re: [PATCH 6.6 and older] uio_hv_generic: Enable user space to
 manage interrupt_mask for subchannels

On Sat, Nov 15, 2025 at 02:29:37PM +0530, Naman Jain wrote:
> From: Long Li <longli@...rosoft.com>
> 
> Enable the user space to manage interrupt_mask for subchannels through
> irqcontrol interface for uio device. Also remove the memory barrier
> when monitor bit is enabled as it is not necessary.
> 
> This is a backport of the upstream commit
> d062463edf17 ("uio_hv_generic: Set event for all channels on the device")
> with some modifications to resolve merge conflicts and take care of
> missing support for slow devices on older kernels.
> Original change was not a fix, but it needs to be backported to fix a
> NULL pointer crash resulting from missing interrupt mask setting.
> 
> Commit 37bd91f22794 ("uio_hv_generic: Let userspace take care of interrupt mask")
> removed the default setting of interrupt_mask for channels (including
> subchannels) in the uio_hv_generic driver, as it relies on the user space
> to take care of managing it. This approach works fine when user space
> can control this setting using the irqcontrol interface provided for uio
> devices. Support for setting the interrupt mask through this interface for
> subchannels came only after commit d062463edf17 ("uio_hv_generic: Set event
> for all channels on the device"). On older kernels, this change is not
> present. With uio_hv_generic no longer setting the interrupt_mask, and
> userspace not having the capability to set it, it remains unset,
> and interrupts can come for the subchannels, which can result in a crash
> in hv_uio_channel_cb. Backport the change to older kernels, where this
> change was not present, to allow userspace to set the interrupt mask
> properly for subchannels. Additionally, this patch also adds certain
> checks for primary vs subchannels in the hv_uio_channel_cb, which can
> gracefully handle these two cases and prevent the NULL pointer crashes.
> 
> Signed-off-by: Long Li <longli@...rosoft.com>
> Fixes: 37bd91f22794 ("uio_hv_generic: Let userspace take care of interrupt mask")

This is a 6.12.y commit id, so a fix for 6.6.y does not make sense :(

> Closes: https://bugs.debian.org/1120602
> Cc: <stable@...r.kernel.org> # 6.6.x and older

How "old" do you want this?  Can you fix the Fixes: line up and resend
with this info?

thanks,

greg k-h