linux-kernel - Re: [PATCH] vfio: platform: Fix using devices in PM Domains

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Date:   Fri, 13 Apr 2018 11:19:54 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Auger Eric <eric.auger@...hat.com>
Cc:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Baptiste Reynal <b.reynal@...tualopensystems.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        KVM list <kvm@...r.kernel.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] vfio: platform: Fix using devices in PM Domains

Hi Eric,

On Fri, Apr 13, 2018 at 11:14 AM, Auger Eric <eric.auger@...hat.com> wrote:
> On 11/04/18 11:24, Geert Uytterhoeven wrote:
>> If a device is part of a PM Domain (e.g. power and/or clock domain), its
>> power state is managed using Runtime PM.  Without Runtime PM, the device
>> may not be powered up, causing subtle failures, crashes, or system
>> lock-ups when the device is accessed by the guest.
> the device may not be powered up/clcoked or power/clock may be switched
> off while the guest uses it.
>>
>> Fix this by adding Runtime PM support, powering the device when the VFIO
>> device is opened by the guest.
>>
>> Note that while more fine-grained power management could be implemented
>> on the guest side, if exported, this would be inherently unsafe, as
>> abusing it may kill the whole system.
>
> Please can you elaborate on this remark please?

If power-management of the device would be delegated to the guest, and the
guest forgets to enable device power before accessing the device's registers,
this could lock up the system, and thus disturb both the host and other guests.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds