linux-kernel - RE: [PATCH] Drivers: hv: vmbus: Disallow the freeze PM operation

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Date:   Wed, 8 Apr 2020 17:43:35 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     vkuznets <vkuznets@...hat.com>
CC:     KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Michael Kelley <mikelley@...rosoft.com>
Subject: RE: [PATCH] Drivers: hv: vmbus: Disallow the freeze PM operation

> From: Vitaly Kuznetsov <vkuznets@...hat.com>
> Sent: Wednesday, April 8, 2020 8:47 AM
> > IMO 'freeze' in a Linux VM on Hyper-V is not really useful in practice,
> > so let's disallow the operation for both Gen-1 and Gen-2 VMs, even if
> > it's not an issue for Gen-1 VMs.
> 
> Suspend-to-idle may not be very useful indeed, however, it worked before
> and I think we can just fix it.

How can we fix Suspend-to-idle for a Gen-2 VM, in which no device can work
as wakeup devices? Note: in the case of Suspend-to-idle, now all the vmbus
devices including the synthetic keyboard/mouse are suspended completely.

Are you suggesting hv_vmbus should distinguish Suspend-to-idle from
hibernation, and for the former hv_vmbus should not suspend the synthetic
keyboard/mouse? This should be doable but IMO this is not a very trivial
effort, and I'm trying to avoid it since IMO Suspend-to-idle is not really 
useful in practice for a Linux VM on Hyper-V. :-)

> In particular, why do we need to do
> anything when we are not hibernating?

Are you suggesting hv_vmbus should not suspend the vmbus devices at all
in the case of Suspend-to-idle?

> > +/*
> > + * Note: "freeze/suspend" here means "systemctl suspend".
> > + * "systemctl hibernate" is still supported.
> 
> Let's not use systemd terminology in kernel, let's use the ones from
> admin-guide/pm/sleep-states.rst (Suspend-to-Idle/Standby/Suspend-to-RAM/
> Hibernation).
> --
> Vitaly

Thanks! I'll use the accurate terms.

Thanks,
-- Dexuan