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Subject: Re: [PATCH v2 01/11] xen/manage: keep track of the on-going suspend
 mode
To:     Anchal Agarwal <anchalag@amazon.com>, tglx@linutronix.de,
        mingo@redhat.com, bp@alien8.de, hpa@zytor.com, x86@kernel.org,
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 <20200702182136.GA3511@dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com>
From:   Boris Ostrovsky <boris.ostrovsky@oracle.com>
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Date:   Mon, 13 Jul 2020 11:52:01 -0400
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On 7/2/20 2:21 PM, Anchal Agarwal wrote:
> From: Munehisa Kamata <kamatam@amazon.com>
>
> Guest hibernation is different from xen suspend/resume/live migration.
> Xen save/restore does not use pm_ops as is needed by guest hibernation.=

> Hibernation in guest follows ACPI path and is guest inititated , the
> hibernation image is saved within guest as compared to later modes
> which are xen toolstack assisted and image creation/storage is in
> control of hypervisor/host machine.
> To differentiate between Xen suspend and PM hibernation, keep track
> of the on-going suspend mode by mainly using a new PM notifier.
> Introduce simple functions which help to know the on-going suspend mode=

> so that other Xen-related code can behave differently according to the
> current suspend mode.
> Since Xen suspend doesn't have corresponding PM event, its main logic
> is modfied to acquire pm_mutex and set the current mode.
>
> Though, acquirng pm_mutex is still right thing to do, we may
> see deadlock if PM hibernation is interrupted by Xen suspend.
> PM hibernation depends on xenwatch thread to process xenbus state
> transactions, but the thread will sleep to wait pm_mutex which is
> already held by PM hibernation context in the scenario. Xen shutdown
> code may need some changes to avoid the issue.
>
> [Anchal Agarwal: Changelog]:
>  RFC v1->v2: Code refactoring
>  v1->v2:     Remove unused functions for PM SUSPEND/PM hibernation
>
> Signed-off-by: Anchal Agarwal <anchalag@amazon.com>
> Signed-off-by: Munehisa Kamata <kamatam@amazon.com>
> ---
>  drivers/xen/manage.c  | 60 +++++++++++++++++++++++++++++++++++++++++++=

>  include/xen/xen-ops.h |  1 +
>  2 files changed, 61 insertions(+)
>
> diff --git a/drivers/xen/manage.c b/drivers/xen/manage.c
> index cd046684e0d1..69833fd6cfd1 100644
> --- a/drivers/xen/manage.c
> +++ b/drivers/xen/manage.c
> @@ -14,6 +14,7 @@
>  #include <linux/freezer.h>
>  #include <linux/syscore_ops.h>
>  #include <linux/export.h>
> +#include <linux/suspend.h>
> =20
>  #include <xen/xen.h>
>  #include <xen/xenbus.h>
> @@ -40,6 +41,20 @@ enum shutdown_state {
>  /* Ignore multiple shutdown requests. */
>  static enum shutdown_state shutting_down =3D SHUTDOWN_INVALID;
> =20
> +enum suspend_modes {
> +	NO_SUSPEND =3D 0,
> +	XEN_SUSPEND,
> +	PM_HIBERNATION,
> +};
> +
> +/* Protected by pm_mutex */
> +static enum suspend_modes suspend_mode =3D NO_SUSPEND;
> +
> +bool xen_is_xen_suspend(void)


Weren't you going to call this pv suspend? (And also --- is this suspend
or hibernation? Your commit messages and cover letter talk about fixing
hibernation).


> +{
> +	return suspend_mode =3D=3D XEN_SUSPEND;
> +}
> +


> +
> +static int xen_pm_notifier(struct notifier_block *notifier,
> +			unsigned long pm_event, void *unused)
> +{
> +	switch (pm_event) {
> +	case PM_SUSPEND_PREPARE:
> +	case PM_HIBERNATION_PREPARE:
> +	case PM_RESTORE_PREPARE:
> +		suspend_mode =3D PM_HIBERNATION;


Do you ever use this mode? It seems to me all you care about is whether
or not we are doing XEN_SUSPEND. And so perhaps suspend_mode could
become a boolean. And then maybe even drop it altogether because it you
should be able to key off (shutting_down =3D=3D SHUTDOWN_SUSPEND).


> +		break;
> +	case PM_POST_SUSPEND:
> +	case PM_POST_RESTORE:
> +	case PM_POST_HIBERNATION:
> +		/* Set back to the default */
> +		suspend_mode =3D NO_SUSPEND;
> +		break;
> +	default:
> +		pr_warn("Receive unknown PM event 0x%lx\n", pm_event);
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +};


> +static int xen_setup_pm_notifier(void)
> +{
> +	if (!xen_hvm_domain())
> +		return -ENODEV;


I forgot --- what did we decide about non-x86 (i.e. ARM)?


And PVH dom0.


-boris