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23 Jul 2020 22:58:05 +0000 Received: from EX13MTAUEE002.ant.amazon.com (iad55-ws-svc-p15-lb9-vlan3.iad.amazon.com [10.40.159.166]) by email-inbound-relay-1d-474bcd9f.us-east-1.amazon.com (Postfix) with ESMTPS id D35D6A1FB9; Thu, 23 Jul 2020 22:57:58 +0000 (UTC) Received: from EX13D08UEE003.ant.amazon.com (10.43.62.118) by EX13MTAUEE002.ant.amazon.com (10.43.62.24) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Thu, 23 Jul 2020 22:57:45 +0000 Received: from EX13MTAUEE002.ant.amazon.com (10.43.62.24) by EX13D08UEE003.ant.amazon.com (10.43.62.118) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Thu, 23 Jul 2020 22:57:45 +0000 Received: from dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com (172.22.96.68) by mail-relay.amazon.com (10.43.62.224) with Microsoft SMTP Server id 15.0.1497.2 via Frontend Transport; Thu, 23 Jul 2020 22:57:45 +0000 Received: by dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com (Postfix, from userid 4335130) id 5F7384CA2B; Thu, 23 Jul 2020 22:57:45 +0000 (UTC) Date: Thu, 23 Jul 2020 22:57:45 +0000 From: Anchal Agarwal To: Stefano Stabellini CC: Boris Ostrovsky , , , , , , , , , , , , , , , , , , , , , , , , , Message-ID: <20200723225745.GB32316@dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com> References: <50298859-0d0e-6eb0-029b-30df2a4ecd63@oracle.com> <20200715204943.GB17938@dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com> <0ca3c501-e69a-d2c9-a24c-f83afd4bdb8c@oracle.com> <20200717191009.GA3387@dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com> <5464f384-d4b4-73f0-d39e-60ba9800d804@oracle.com> <20200721000348.GA19610@dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com> <408d3ce9-2510-2950-d28d-fdfe8ee41a54@oracle.com> <20200722180229.GA32316@dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-Rspamd-Queue-Id: BA8A918049B69 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Jul 22, 2020 at 04:49:16PM -0700, Stefano Stabellini wrote: > CAUTION: This email originated from outside of the organization. Do not= click links or open attachments unless you can confirm the sender and kn= ow the content is safe. >=20 >=20 >=20 > On Wed, 22 Jul 2020, Anchal Agarwal wrote: > > On Tue, Jul 21, 2020 at 05:18:34PM -0700, Stefano Stabellini wrote: > > > On Tue, 21 Jul 2020, Boris Ostrovsky wrote: > > > > >>>>>> +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=E2=80=99ll 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 the= re). > > > > >>>> > > > > >>>> > > > > >>> Ok makes sense. TBH, I haven't tested this part of code on AR= M 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 hi= bernation > > > > >> 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 wit= h 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 s= upport 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 i= s needed is to > > > > > fix Xen side of things. > > > > > > > > > > I am not sure what could be done to achieve any assurances on a= rm side as far as > > > > > this series is concerned. > > > > > > Just to clarify: new features don't need to work on ARM or cause an= y > > > addition efforts to you to make them work on ARM. The patch series = only > > > needs not to break existing code paths (on ARM and any other platfo= rms). > > > It should also not make it overly difficult to implement the ARM si= de of > > > things (if there is one) at some point in the future. > > > > > > FYI drivers/xen/manage.c is compiled and working on ARM today, howe= ver > > > Xen suspend/resume is not supported. I don't know for sure if > > > guest-initiated hibernation works because I have not tested it. > > > > > > > > > > > > > If you are not sure what the effects are (or sure that it won't w= ork) 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. Howe= ver, > > > in this specific case there is nothing in this patch that doesn't w= ork > > > 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_o= ps > > callbacks registration. > > > 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 an= y > > > trouble on ARM. The two main x86-specific functions are > > > xen_syscore_suspend/resume and they look trivial to implement on AR= M (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 t= o 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 correc= tly. > > These callbacks takes care of xen primitives like shared_info_page, > > grant table, sched clock, runstate time which are important to save t= he 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 th= ere for at driver > > level. >=20 > I meant the other way around :-) Let me rephrase the question. >=20 > Do you think that implementing freeze/thaw/restore at the driver level > without having xen_syscore_suspend/resume can potentially make things > worse compared to not having freeze/thaw/restore at the driver level at > all? I think in both the cases I don't expect it to work. System may end up in different state if you register vs not. Hibernation does not work properl= y at least for domU instances without these changes on x86 and I am assumin= g the same for ARM. If you do not register freeze/thaw/restore callbacks for arm, then on invocation of xenbus_dev_suspend, default suspend/resume callbacks will be called for each driver and since you do not have any code to save= domU's xen primitives state (syscore_ops), hibernation will either fail or will = demand a reboot. I do no have setup to test the current state of ARM's hibernation If you only register freeze/thaw/restore and no syscore_ops, it will agai= n fail. Since, I do not have an ARM setup running, I quickly ran a similar test o= n x86, may not be an apple to apple comparison but instance failed to resume or = I should say stuck showing huge jump in time and required a reboot. Now if this doesn't happen currently when you trigger hibernation on arm = domU instances or if system is still alive when you trigger hibernation in xen= guest then not registering the callbacks may be a better idea. In that case ma= y be=20 I need to put arch specific check when registering freeze/thaw/restore ha= ndlers. Hope that answers your question. Thanks, Anchal