* RE: [PATCH v2 1/2] Drivers: hv: vmbus: Provide option to skip VMBus unload on panic
[not found] <20260217182335.265585-1-mhklkml@zohomail.com>
@ 2026-05-04 20:47 ` Michael Kelley
2026-05-13 22:32 ` Wei Liu
0 siblings, 1 reply; 2+ messages in thread
From: Michael Kelley @ 2026-05-04 20:47 UTC (permalink / raw)
To: wei.liu@kernel.org, tzimmermann@suse.de, longli@microsoft.com,
jfalempe@redhat.com
Cc: drawat.floss@gmail.com, maarten.lankhorst@linux.intel.com,
mripard@kernel.org, airlied@gmail.com, simona@ffwll.ch,
kys@microsoft.com, haiyangz@microsoft.com, decui@microsoft.com,
ryasuoka@redhat.com, dri-devel@lists.freedesktop.org,
linux-kernel@vger.kernel.org, linux-hyperv@vger.kernel.org,
stable@vger.kernel.org
From: Michael Kelley <mhklkml@zohomail.com> Sent: Tuesday, February 17, 2026 10:24 AM
>
Wei and Thomas --
This small patch series has been neglected. Patch 2 of the series is here [1].
Long Li < longli@microsoft.com> has given a Reviewed-by on this patch,
and Jocelyn Falempe <jfalempe@redhat.com> has given a Reviewed-by
on Patch 2 of the series, modulo a comment which I have incorporated.
See [2]. But I neglected to add her R-b when I spun v2 of the series.
Any reason this can't be picked up as a bug fix for 7.1? I just checked,
and it applies cleanly to a recent linux-next (20260423). I'd suggest
going through the hyperv tree, as these two patches should be kept
together in sequence.
Michael
[1] https://lore.kernel.org/linux-hyperv/20260217182335.265585-2-mhklkml@zohomail.com/
[2] https://lore.kernel.org/linux-hyperv/a5372b72-8dc0-4f2d-ad5c-086f3e75ee81@redhat.com/
> Currently, VMBus code initiates a VMBus unload in the panic path so
> that if a kdump kernel is loaded, it can start fresh in setting up its
> own VMBus connection. However, a driver for the VMBus virtual frame
> buffer may need to flush dirty portions of the frame buffer back to
> the Hyper-V host so that panic information is visible in the graphics
> console. To support such flushing, provide exported functions for the
> frame buffer driver to specify that the VMBus unload should not be
> done by the VMBus driver, and to initiate the VMBus unload itself.
> Together these allow a frame buffer driver to delay the VMBus unload
> until after it has completed the flush.
>
> Ideally, the VMBus driver could use its own panic-path callback to do
> the unload after all frame buffer drivers have finished. But DRM frame
> buffer drivers use the kmsg dump callback, and there are no callbacks
> after that in the panic path. Hence this somewhat messy approach to
> properly sequencing the frame buffer flush and the VMBus unload.
>
> Fixes: 3671f3777758 ("drm/hyperv: Add support for drm_panic")
> Signed-off-by: Michael Kelley <mhklinux@outlook.com>
> ---
> Changes in v2: None
>
> drivers/hv/channel_mgmt.c | 1 +
> drivers/hv/hyperv_vmbus.h | 1 -
> drivers/hv/vmbus_drv.c | 25 ++++++++++++++++++-------
> include/linux/hyperv.h | 3 +++
> 4 files changed, 22 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
> index 74fed2c073d4..5de83676dbad 100644
> --- a/drivers/hv/channel_mgmt.c
> +++ b/drivers/hv/channel_mgmt.c
> @@ -944,6 +944,7 @@ void vmbus_initiate_unload(bool crash)
> else
> vmbus_wait_for_unload();
> }
> +EXPORT_SYMBOL_GPL(vmbus_initiate_unload);
>
> static void vmbus_setup_channel_state(struct vmbus_channel *channel,
> struct vmbus_channel_offer_channel *offer)
> diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
> index cdbc5f5c3215..5d3944fc93ae 100644
> --- a/drivers/hv/hyperv_vmbus.h
> +++ b/drivers/hv/hyperv_vmbus.h
> @@ -440,7 +440,6 @@ void hv_vss_deinit(void);
> int hv_vss_pre_suspend(void);
> int hv_vss_pre_resume(void);
> void hv_vss_onchannelcallback(void *context);
> -void vmbus_initiate_unload(bool crash);
>
> static inline void hv_poll_channel(struct vmbus_channel *channel,
> void (*cb)(void *))
> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> index 6785ad63a9cb..97dfa529d250 100644
> --- a/drivers/hv/vmbus_drv.c
> +++ b/drivers/hv/vmbus_drv.c
> @@ -69,19 +69,29 @@ bool vmbus_is_confidential(void)
> }
> EXPORT_SYMBOL_GPL(vmbus_is_confidential);
>
> +static bool skip_vmbus_unload;
> +
> +/*
> + * Allow a VMBus framebuffer driver to specify that in the case of a panic,
> + * it will do the VMbus unload operation once it has flushed any dirty
> + * portions of the framebuffer to the Hyper-V host.
> + */
> +void vmbus_set_skip_unload(bool skip)
> +{
> + skip_vmbus_unload = skip;
> +}
> +EXPORT_SYMBOL_GPL(vmbus_set_skip_unload);
> +
> /*
> * The panic notifier below is responsible solely for unloading the
> * vmbus connection, which is necessary in a panic event.
> - *
> - * Notice an intrincate relation of this notifier with Hyper-V
> - * framebuffer panic notifier exists - we need vmbus connection alive
> - * there in order to succeed, so we need to order both with each other
> - * [see hvfb_on_panic()] - this is done using notifiers' priorities.
> */
> static int hv_panic_vmbus_unload(struct notifier_block *nb, unsigned long val,
> void *args)
> {
> - vmbus_initiate_unload(true);
> + if (!skip_vmbus_unload)
> + vmbus_initiate_unload(true);
> +
> return NOTIFY_DONE;
> }
> static struct notifier_block hyperv_panic_vmbus_unload_block = {
> @@ -2848,7 +2858,8 @@ static void hv_crash_handler(struct pt_regs *regs)
> {
> int cpu;
>
> - vmbus_initiate_unload(true);
> + if (!skip_vmbus_unload)
> + vmbus_initiate_unload(true);
> /*
> * In crash handler we can't schedule synic cleanup for all CPUs,
> * doing the cleanup for current CPU only. This should be sufficient
> diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
> index dfc516c1c719..b0502a336eb3 100644
> --- a/include/linux/hyperv.h
> +++ b/include/linux/hyperv.h
> @@ -1334,6 +1334,9 @@ int vmbus_allocate_mmio(struct resource **new, struct
> hv_device *device_obj,
> bool fb_overlap_ok);
> void vmbus_free_mmio(resource_size_t start, resource_size_t size);
>
> +void vmbus_initiate_unload(bool crash);
> +void vmbus_set_skip_unload(bool skip);
> +
> /*
> * GUID definitions of various offer types - services offered to the guest.
> */
> --
> 2.25.1
>
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