netdev - Re: [PATCH 04/12] x86/xen: add system core suspend and resume callbacks

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Date:   Wed, 3 Jun 2020 22:40:15 +0000
From:   "Agarwal, Anchal" <anchalag@...zon.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>, "hpa@...or.com" <hpa@...or.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "jgross@...e.com" <jgross@...e.com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Kamata, Munehisa" <kamatam@...zon.com>,
        "sstabellini@...nel.org" <sstabellini@...nel.org>,
        "konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
        "roger.pau@...rix.com" <roger.pau@...rix.com>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>,
        "len.brown@...el.com" <len.brown@...el.com>,
        "pavel@....cz" <pavel@....cz>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "Valentin, Eduardo" <eduval@...zon.com>,
        "Singh, Balbir" <sblbir@...zon.com>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Woodhouse, David" <dwmw@...zon.co.uk>,
        "benh@...nel.crashing.org" <benh@...nel.crashing.org>,
        "Agarwal, Anchal" <anchalag@...zon.com>
Subject: Re: [PATCH 04/12] x86/xen: add system core suspend and resume callbacks

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    On 5/19/20 7:26 PM, Anchal Agarwal wrote:
    > From: Munehisa Kamata <kamatam@...zon.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 calls syscore_suspend from xen_suspend
So, if these syscore ops gets called  during xen_suspend do not do anything. Check if the mode is in xen suspend 
and return from there. These syscore_ops are specifically for domU hibernation.
I must admit, I may have overlooked lack of explanation of some implicit details in the original commit msg. 

    >  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;
    > +
    > +     xrfp.domid = DOMID_SELF;
    > +     xrfp.gpfn = __pa(HYPERVISOR_shared_info) >> PAGE_SHIFT;
    > +
    > +     ret = HYPERVISOR_memory_op(XENMEM_remove_from_physmap, &xrfp);
    > +     if (!ret)
    > +             HYPERVISOR_shared_info = &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 applicable for PV guests right?

    > +}
    > +
    > +/*
    > + * These callbacks will be called with interrupts disabled and when having only
    > + * one CPU online.
    > + */
    > +static struct syscore_ops xen_hvm_syscore_ops = {
    > +     .suspend = xen_syscore_suspend,
    > +     .resume = xen_syscore_resume
    > +};
    > +
    > +void __init xen_setup_syscore_ops(void)
    > +{
    > +     if (xen_hvm_domain())


    Have you tested this (the whole feature, not just this patch) with PVH
    guest BTW? And PVH dom0 for that matter?

No I haven't. The whole series is just tested with hvm/pvhvm guests.

    -boris
Thanks,
Anchal

    > +             register_syscore_ops(&xen_hvm_syscore_ops);
    > +}