netdev - Re: [PATCH v3 01/11] xen/manage: keep track of the on-going suspend mode

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Date:   Tue, 1 Jun 2021 10:18:36 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Anchal Agarwal <anchalag@...zon.com>
Cc:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>, "hpa@...or.com" <hpa@...or.com>,
        "jgross@...e.com" <jgross@...e.com>,
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        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "sstabellini@...nel.org" <sstabellini@...nel.org>,
        "konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
        "roger.pau@...rix.com" <roger.pau@...rix.com>,
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        "pavel@....cz" <pavel@....cz>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
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        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dwmw@...zon.co.uk
Subject: Re: [PATCH v3 01/11] xen/manage: keep track of the on-going suspend
 mode


On 5/28/21 5:50 PM, Anchal Agarwal wrote:

> That only fails during boot but not after the control jumps into the image. The
> non boot cpus are brought offline(freeze_secondary_cpus) and then online via cpu hotplug path. In that case xen_vcpu_setup doesn't invokes the hypercall again.


OK, that makes sense --- by that time VCPUs have already been registered. What I don't understand though is why resume doesn't fail every time --- xen_vcpu and xen_vcpu_info should be different practically always, shouldn't they? Do you observe successful resumes when the hypercall fails?


>
> Another line of thought is something what kexec does to come around this problem
> is to abuse soft_reset and issue it during syscore_resume or may be before the image get loaded.
> I haven't experimented with that yet as I am assuming there has to be a way to re-register vcpus during resume.


Right, that sounds like it should work.


-boris