linux-kernel - Re: [PATCH v4 02/17] x86/acrn: Introduce acrn_{setup, remove}_intr

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Date:   Wed, 30 Sep 2020 11:02:44 +0800
From:   Shuo A Liu <shuo.a.liu@...el.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
        x86@...nel.org, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "H . Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Yu Wang <yu1.wang@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Yakui Zhao <yakui.zhao@...el.com>,
        Zhi Wang <zhi.a.wang@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Fengwei Yin <fengwei.yin@...el.com>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>
Subject: Re: [PATCH v4 02/17] x86/acrn: Introduce acrn_{setup,
 remove}_intr_handler()

Hi Boris,

On Tue 29.Sep'20 at 22:26:54 +0200, Borislav Petkov wrote:
>On Tue, Sep 29, 2020 at 10:07:17PM +0200, Thomas Gleixner wrote:
>> That does not prevent that either and notifiers suck.
>
>Bah, atomic notifiers run functions which cannot block, not what is
>needed here, right.
>
>> The pointer is fine and if something removes the handler before all of
>> the muck is shutdown then the author can keep the pieces and mop up
>> the remains.
>
>Uhu, so what makes sure that the module is not removed while an IRQ is
>happening?

The precondition of the removing of the module is that there is no
User VM living (every opening of the dev file will hold a ref count of
the module). The interrupt only can occur with active User VMs. So if
a notification interrupt is happending, the module cannot be removed as
there is still User VM living.

Thanks
shuo