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Date:   Tue, 21 Jul 2020 17:48:45 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Anchal Agarwal <anchalag@...zon.com>
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, sstabellini@...nel.org,
        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


>>>>>> +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)?
>>>>> It would be great to support that however, its  out of
>>>>> scope for this patch set.
>>>>> I’ll be happy to discuss it separately.
>>>>
>>>> I wasn't implying that this *should* work on ARM but rather whether this
>>>> will break ARM somehow (because xen_hvm_domain() is true there).
>>>>
>>>>
>>> Ok makes sense. TBH, I haven't tested this part of code on ARM and the series
>>> was only support x86 guests hibernation.
>>> Moreover, this notifier is there to distinguish between 2 PM
>>> events PM SUSPEND and PM hibernation. Now since we only care about PM
>>> HIBERNATION I may just remove this code and rely on "SHUTDOWN_SUSPEND" state.
>>> However, I may have to fix other patches in the series where this check may
>>> appear and cater it only for x86 right?
>>
>>
>> I don't know what would happen if ARM guest tries to handle hibernation
>> callbacks. The only ones that you are introducing are in block and net
>> fronts and that's arch-independent.
>>
>>
>> You do add a bunch of x86-specific code though (syscore ops), would
>> something similar be needed for ARM?
>>
>>
> I don't expect this to work out of the box on ARM. To start with something
> similar will be needed for ARM too.
> We may still want to keep the driver code as-is.
> 
> I understand the concern here wrt ARM, however, currently the support is only
> proposed for x86 guests here and similar work could be carried out for ARM.
> Also, if regular hibernation works correctly on arm, then all is needed is to
> fix Xen side of things.
> 
> I am not sure what could be done to achieve any assurances on arm side as far as
> this series is concerned.


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;


(plus '|| xen_initial_domain()' for PVH dom0 as Roger suggested.)

-boris

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