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Subject: Re: [PATCH 04/12] x86/xen: add system core suspend and resume
 callbacks
To:     "Agarwal, Anchal" <anchalag@amazon.com>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "bp@alien8.de" <bp@alien8.de>, "hpa@zytor.com" <hpa@zytor.com>,
        "x86@kernel.org" <x86@kernel.org>,
        "jgross@suse.com" <jgross@suse.com>,
        "linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "Kamata, Munehisa" <kamatam@amazon.com>,
        "sstabellini@kernel.org" <sstabellini@kernel.org>,
        "konrad.wilk@oracle.com" <konrad.wilk@oracle.com>,
        "roger.pau@citrix.com" <roger.pau@citrix.com>,
        "axboe@kernel.dk" <axboe@kernel.dk>,
        "davem@davemloft.net" <davem@davemloft.net>,
        "rjw@rjwysocki.net" <rjw@rjwysocki.net>,
        "len.brown@intel.com" <len.brown@intel.com>,
        "pavel@ucw.cz" <pavel@ucw.cz>,
        "peterz@infradead.org" <peterz@infradead.org>,
        "Valentin, Eduardo" <eduval@amazon.com>,
        "Singh, Balbir" <sblbir@amazon.com>,
        "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
        "vkuznets@redhat.com" <vkuznets@redhat.com>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Woodhouse, David" <dwmw@amazon.co.uk>,
        "benh@kernel.crashing.org" <benh@kernel.crashing.org>
References: <cover.1589926004.git.anchalag@amazon.com>
 <79cf02631dc00e62ebf90410bfbbdb52fe7024cb.1589926004.git.anchalag@amazon.com>
 <4b577564-e4c3-0182-2b9e-5f79004f32a1@oracle.com>
 <B966B3A2-4F08-42FA-AF59-B8AA0783C2BA@amazon.com>
From:   Boris Ostrovsky <boris.ostrovsky@oracle.com>
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Date:   Fri, 5 Jun 2020 17:24:37 -0400
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On 6/3/20 6:40 PM, Agarwal, Anchal wrote:
>     CAUTION: This email originated from outside of the organization. Do=
 not click links or open attachments unless you can confirm the sender an=
d know the content is safe.
>
>
>
>     On 5/19/20 7:26 PM, Anchal Agarwal wrote:
>     > From: Munehisa Kamata <kamatam@amazon.com>
>     >
>     > Add Xen PVHVM specific system core callbacks for PM suspend and
>     > hibernation support. The callbacks suspend and resume Xen
>     > primitives,like shared_info, pvclock and grant table. Note that
>     > Xen suspend can handle them in a different manner, but system
>     > core callbacks are called from the context.
>
>
>     I don't think I understand that last sentence.
>
> Looks like it may have cryptic meaning of stating that xen_suspend call=
s syscore_suspend from xen_suspend
> So, if these syscore ops gets called  during xen_suspend do not do anyt=
hing. Check if the mode is in xen suspend=20
> and return from there. These syscore_ops are specifically for domU hibe=
rnation.
> I must admit, I may have overlooked lack of explanation of some implici=
t details in the original commit msg.=20
>
>     >  So if the callbacks
>     > are called from Xen suspend context, return immediately.
>     >
>
>
>     > +
>     > +static int xen_syscore_suspend(void)
>     > +{
>     > +     struct xen_remove_from_physmap xrfp;
>     > +     int ret;
>     > +
>     > +     /* Xen suspend does similar stuffs in its own logic */
>     > +     if (xen_suspend_mode_is_xen_suspend())
>     > +             return 0;


With your explanation now making this clearer, is this check really
necessary? From what I see we are in XEN_SUSPEND mode when
lock_system_sleep() lock is taken, meaning that we can't initialize
hibernation.


>     > +
>     > +     xrfp.domid =3D DOMID_SELF;
>     > +     xrfp.gpfn =3D __pa(HYPERVISOR_shared_info) >> PAGE_SHIFT;
>     > +
>     > +     ret =3D HYPERVISOR_memory_op(XENMEM_remove_from_physmap, &x=
rfp);
>     > +     if (!ret)
>     > +             HYPERVISOR_shared_info =3D &xen_dummy_shared_info;
>     > +
>     > +     return ret;
>     > +}
>     > +
>     > +static void xen_syscore_resume(void)
>     > +{
>     > +     /* Xen suspend does similar stuffs in its own logic */
>     > +     if (xen_suspend_mode_is_xen_suspend())
>     > +             return;
>     > +
>     > +     /* No need to setup vcpu_info as it's already moved off */
>     > +     xen_hvm_map_shared_info();
>     > +
>     > +     pvclock_resume();
>     > +
>     > +     gnttab_resume();
>
>
>     Do you call gnttab_suspend() in pm suspend path?
> No, since it does nothing for HVM guests. The unmap_frames is only appl=
icable for PV guests right?


You should call it nevertheless. It will decide whether or not anything
needs to be done.


-boris