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

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Date:   Sat, 18 Jul 2020 21:47:04 -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

(Roger, question for you at the very end)

On 7/17/20 3:10 PM, Anchal Agarwal wrote:
> On Wed, Jul 15, 2020 at 05:18:08PM -0400, Boris Ostrovsky wrote:
>> CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.
>>
>>
>>
>> On 7/15/20 4:49 PM, Anchal Agarwal wrote:
>>> On Mon, Jul 13, 2020 at 11:52:01AM -0400, Boris Ostrovsky wrote:
>>>> CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.
>>>>
>>>>
>>>>
>>>> On 7/2/20 2:21 PM, Anchal Agarwal wrote:
>>>>> +
>>>>> +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).
>>>>
>>>>
>>> This is for hibernation is for pvhvm/hvm/pv-on-hvm guests as you may call it.
>>> The method is just there to check if "xen suspend" is in progress.
>>> I do not see "xen_suspend" differentiating between pv or hvm
>>> domain until later in the code hence, I abstracted it to xen_is_xen_suspend.
>>
>> I meant "pv suspend" in the sense that this is paravirtual suspend, not
>> suspend for paravirtual guests. Just like pv drivers are for both pv and
>> hvm guests.
>>
>>
>> And then --- should it be pv suspend or pv hibernation?
>>
>>
> Ok so I think I am lot confused by this question. Here is what this
> function for, function xen_is_xen_suspend() just tells us whether 
> the guest is in "SHUTDOWN_SUSPEND" state or not. This check is needed
> for correct invocation of syscore_ops callbacks registered for guest's
> hibernation and for xenbus to invoke respective callbacks[suspend/resume
> vs freeze/thaw/restore].
> Since "shutting_down" state is defined static and is not directly available
> to other parts of the code, the function solves the purpose.
>
> I am having hard time understanding why this should be called pv
> suspend/hibernation unless you are suggesting something else?
> Am I missing your point here? 



I think I understand now what you are trying to say --- it's whether we
are going to use xen_suspend() routine, right? If that's the case then
sure, you can use "xen_suspend" term. (I'd probably still change
xen_is_xen_suspend() to is_xen_suspend())


>>>>> +{
>>>>> +     return suspend_mode == XEN_SUSPEND;
>>>>> +}
>>>>> +
>>>> +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?


>>>> And PVH dom0.
>>> That's another good use case to make it work with however, I still
>>> think that should be tested/worked upon separately as the feature itself
>>> (PVH Dom0) is very new.
>>
>> Same question here --- will this break PVH dom0?
>>
> I haven't tested it as a part of this series. Is that a blocker here?


I suspect dom0 will not do well now as far as hibernation goes, in which
case you are not breaking anything.


Roger?


-boris