netdev - Re: [PATCH v2 01/11] xen/manage: keep track of the on-going suspend mode

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Date:   Wed, 22 Jul 2020 18:45:47 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Anchal Agarwal <anchalag@...zon.com>,
        Stefano Stabellini <sstabellini@...nel.org>
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        x86@...nel.org, jgross@...e.com, linux-pm@...r.kernel.org,
        linux-mm@...ck.org, kamatam@...zon.com, konrad.wilk@...cle.com,
        roger.pau@...rix.com, axboe@...nel.dk, davem@...emloft.net,
        rjw@...ysocki.net, len.brown@...el.com, pavel@....cz,
        peterz@...radead.org, eduval@...zon.com, sblbir@...zon.com,
        xen-devel@...ts.xenproject.org, vkuznets@...hat.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        dwmw@...zon.co.uk, benh@...nel.crashing.org
Subject: Re: [PATCH v2 01/11] xen/manage: keep track of the on-going suspend
 mode

On 7/22/20 2:02 PM, Anchal Agarwal wrote:
> On Tue, Jul 21, 2020 at 05:18:34PM -0700, Stefano Stabellini wrote:
>>
>>
>>> If you are not sure what the effects are (or sure that it won't work) on
>>> ARM then I'd add IS_ENABLED(CONFIG_X86) check, i.e.
>>>
>>>
>>> if (!IS_ENABLED(CONFIG_X86) || !xen_hvm_domain())
>>>       return -ENODEV;
>> That is a good principle to have and thanks for suggesting it. However,
>> in this specific case there is nothing in this patch that doesn't work
>> on ARM. From an ARM perspective I think we should enable it and
>> &xen_pm_notifier_block should be registered.
>>
> This question is for Boris, I think you we decided to get rid of the notifier
> in V3 as all we need  to check is SHUTDOWN_SUSPEND state which sounds plausible
> to me. So this check may go away. It may still be needed for sycore_ops
> callbacks registration.


If this check is going away then I guess there is nothing to do here.


My concern isn't about this particular notifier but rather whether this
feature may affect existing functionality (ARM and PVH dom0). If Stefano
feels this should be fine for ARM then so be it.


-boris


>> Given that all guests are HVM guests on ARM, it should work fine as is.
>>
>>
>> I gave a quick look at the rest of the series and everything looks fine
>> to me from an ARM perspective. I cannot imaging that the new freeze,
>> thaw, and restore callbacks for net and block are going to cause any
>> trouble on ARM. The two main x86-specific functions are
>> xen_syscore_suspend/resume and they look trivial to implement on ARM (in
>> the sense that they are likely going to look exactly the same.)
>>
> Yes but for now since things are not tested I will put this
> !IS_ENABLED(CONFIG_X86) on syscore_ops calls registration part just to be safe
> and not break anything.
>> One question for Anchal: what's going to happen if you trigger a
>> hibernation, you have the new callbacks, but you are missing
>> xen_syscore_suspend/resume?
>>
>> Is it any worse than not having the new freeze, thaw and restore
>> callbacks at all and try to do a hibernation?
> If callbacks are not there, I don't expect hibernation to work correctly.
> These callbacks takes care of xen primitives like shared_info_page,
> grant table, sched clock, runstate time which are important to save the correct
> state of the guest and bring it back up. Other patches in the series, adds all
> the logic to these syscore callbacks. Freeze/thaw/restore are just there for at driver
> level.
>
> Thanks,
> Anchal