linux-kernel - Re: [PATCH 6.12] uio_hv_generic: Set event for all channels on the device

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Message-ID: <dca120db-4751-4de8-961e-05ba701ca100@linux.microsoft.com>
Date: Sat, 15 Nov 2025 14:32:41 +0530
From: Naman Jain <namjain@...ux.microsoft.com>
To: Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Michael Kelley <mhklinux@...look.com>, Long Li <longli@...rosoft.com>,
 Saurabh Sengar <ssengar@...ux.microsoft.com>
Cc: "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 6.12] uio_hv_generic: Set event for all channels on the
 device



On 11/15/2025 2:27 PM, Naman Jain wrote:
> From: Long Li <longli@...rosoft.com>
> 
> Hyper-V may offer a non latency sensitive device with subchannels without
> monitor bit enabled. The decision is entirely on the Hyper-V host not
> configurable within guest.
> 
> When a device has subchannels, also signal events for the subchannel
> if its monitor bit is disabled.
> 
> This patch also removes the memory barrier when monitor bit is enabled
> as it is not necessary. The memory barrier is only needed between
> setting up interrupt mask and calling vmbus_set_event() when monitor
> bit is disabled.
> 
> This is a backport of the upstream commit
> d062463edf17 ("uio_hv_generic: Set event for all channels on the device")
> with minor modifications to resolve merge conflicts.
> 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>
> Reviewed-by: Michael Kelley <mhklinux@...look.com>
> Reviewed-by: Saurabh Sengar <ssengar@...ux.microsoft.com>
> Fixes: 37bd91f22794 ("uio_hv_generic: Let userspace take care of interrupt mask")

Sorry for missing this, please add Closes tag, if possible before merging.

Closes: https://bugs.debian.org/1120602

I have kept it in the other patch for 6.6 and prior kernels.

Regards,
Naman

> Cc: <stable@...r.kernel.org> # 6.12.x
> Signed-off-by: Naman Jain <namjain@...ux.microsoft.com>
> ---

Regards,
Naman