linux-kernel - Re: [patch 00/53] x86/topology: The final installment

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Date:   Tue, 8 Aug 2023 12:20:29 +0100
From:   Andrew Cooper <andrew.cooper3@...rix.com>
To:     Juergen Gross <jgross@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Tom Lendacky <thomas.lendacky@....com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Huang Rui <ray.huang@....com>,
        Dimitri Sivanich <dimitri.sivanich@....com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Sohil Mehta <sohil.mehta@...el.com>,
        K Prateek Nayak <kprateek.nayak@....com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Zhang Rui <rui.zhang@...el.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Feng Tang <feng.tang@...el.com>,
        Andy Shevchenko <andy@...radead.org>
Subject: Re: [patch 00/53] x86/topology: The final installment

On 08/08/2023 8:40 am, Juergen Gross wrote:
> Tested on an Intel system with Xen:
>
> - PV dom0 is working fine. I couldn't test physical cpu hotplug, but
> removing
>   and then re-adding vcpus to dom0 worked.

It turns out that physical CPU hotplug with XenPV is broken in at least
two ways.

It's dom0 (not Xen) that gets the hot-unplug event, after which the Xen
code in Linux succumbs to a preempt-check failure while trying to
offline the vCPU that aliases the pCPU wanting to go offline.

~Andrew