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Subject: Re: [PATCH] xen/cpuhotplug: Fix initial CPU offlining for PV(H)
 guests
To:     Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org
Cc:     sstabellini@kernel.org
References: <1588976923-3667-1-git-send-email-boris.ostrovsky@oracle.com>
From:   =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= <jgross@suse.com>
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Date:   Mon, 11 May 2020 10:16:07 +0200
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On 09.05.20 00:28, Boris Ostrovsky wrote:
> Commit a926f81d2f6c ("xen/cpuhotplug: Replace cpu_up/down() with
> device_online/offline()") replaced cpu_down() with device_offline()
> call which requires that the CPU has been registered before. This
> registration, however, happens later from topology_init() which
> is called as subsys_initcall(). setup_vcpu_hotplug_event(), on the
> other hand, is invoked earlier, during arch_initcall().
> 
> As result, booting a PV(H) guest with vcpus < maxvcpus causes a crash.
> 
> Move setup_vcpu_hotplug_event() (and therefore setup_cpu_watcher()) to
> late_initcall(). In addition, instead of performing all offlining steps
> in setup_cpu_watcher() simply call disable_hotplug_cpu().
> 
> Fixes: a926f81d2f6c (xen/cpuhotplug: Replace cpu_up/down() with device_online/offline()"
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

Reviewed-by: Juergen Gross <jgross@suse.com>


Juergen