From: mst@redhat.com (Michael S. Tsirkin)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] kvm: pass the virtual SEI syndrome to guest OS
Date: Wed, 29 Mar 2017 16:54:41 +0300 [thread overview]
Message-ID: <20170329164811-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <756e3032-e619-a70d-3e29-d2797e52fecf@redhat.com>
On Wed, Mar 29, 2017 at 03:36:59PM +0200, Laszlo Ersek wrote:
> On 03/29/17 14:51, Michael S. Tsirkin wrote:
> > On Wed, Mar 29, 2017 at 01:58:29PM +0200, Laszlo Ersek wrote:
> >> (8) When QEMU gets SIGBUS from the kernel -- I hope that's going to come
> >> through a signalfd -- QEMU can format the CPER right into guest memory,
> >> and then inject whatever interrupt (or assert whatever GPIO line) is
> >> necessary for notifying the guest.
> >
> > I think I see a race condition potential - what if guest accesses
> > CPER in guest memory while it's being written?
>
> I'm not entirely sure about the data flow here (these parts of the ACPI
> spec are particularly hard to read...), but I thought the OS wouldn't
> look until it got a notification.
There could be multiple notifications, OS might be looking
there because of them.
> Or, are you concerned about the next CPER write by QEMU, while the OS is
> reading the last one (and maybe the CPER area could wrap around?)
>
> >
> > We can probably use another level of indirection to fix this:
> >
> > allocate twice the space, add a pointer to where the valid
> > table is located and update that after writing CPER completely.
> > The pointer can be written atomically but also needs to
> > be read atomically, so I suspect it should be a single byte
> > as we don't know how are OSPMs implementing this.
> >
>
> A-B-A problem? (Is that usually solved with a cookie or a wider
> generation counter? But that would again require wider atomics.)
>
> I do wonder though how this is handled on physical hardware. Assuming
> the hardware error traps to the firmware first (which, on phys hw, is
> responsible for depositing the CPER), in that scenario the phys firmware
> would face the same issue (i.e., asynchronously interrupting the OS,
> which could be reading the previously stored CPER).
>
> Thanks,
> Laszlo
ACPI spec seems to specify a set of serialization actions. I'm guessing
this is what you need to use to avoid changing guest state
while it's reading entries.
--
MST
next prev parent reply other threads:[~2017-03-29 13:54 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-20 7:55 [PATCH] kvm: pass the virtual SEI syndrome to guest OS Dongjiu Geng
2017-03-20 11:24 ` Marc Zyngier
2017-03-20 12:28 ` gengdongjiu
2017-03-20 13:58 ` Marc Zyngier
2017-03-20 15:08 ` James Morse
2017-03-21 6:32 ` gengdongjiu
2017-03-21 11:34 ` Christoffer Dall
2017-03-21 19:11 ` James Morse
2017-03-21 19:39 ` Christoffer Dall
2017-03-21 22:10 ` Peter Maydell
2017-03-22 11:15 ` Marc Zyngier
2017-03-28 10:48 ` James Morse
2017-03-28 11:23 ` Christoffer Dall
2017-03-28 11:33 ` Peter Maydell
2017-03-28 13:27 ` James Morse
2017-03-28 11:54 ` Achin Gupta
2017-03-28 12:16 ` gengdongjiu
2017-03-28 13:40 ` James Morse
2017-03-29 9:36 ` gengdongjiu
2017-03-29 10:36 ` Achin Gupta
2017-03-29 11:58 ` Laszlo Ersek
2017-03-29 12:51 ` Michael S. Tsirkin
2017-03-29 13:36 ` Laszlo Ersek
2017-03-29 13:54 ` Michael S. Tsirkin [this message]
2017-03-29 13:56 ` Punit Agrawal
2017-04-06 12:35 ` gengdongjiu
2017-04-06 18:55 ` Laszlo Ersek
2017-04-07 2:52 ` gengdongjiu
2017-04-07 9:21 ` Laszlo Ersek
2017-04-21 13:27 ` gengdongjiu
2017-04-24 11:27 ` Laszlo Ersek
2017-03-29 14:36 ` gengdongjiu
2017-03-29 14:48 ` Christoffer Dall
2017-03-29 15:37 ` Laszlo Ersek
2017-03-29 17:44 ` Christoffer Dall
2017-03-30 1:22 ` gengdongjiu
2017-03-28 12:22 ` Christoffer Dall
2017-03-28 13:24 ` Achin Gupta
2017-03-28 13:40 ` Christoffer Dall
2017-03-21 13:10 ` James Morse
2017-03-22 13:37 ` gengdongjiu
2017-03-22 18:56 ` James Morse
2017-03-21 6:07 ` gengdongjiu
2017-03-21 13:51 ` kbuild test robot
2017-03-22 3:20 ` gengdongjiu
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