From: Scott Wood <scottwood@freescale.com>
To: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Bharat Bhushan <r65777@freescale.com>, <kvm-ppc@vger.kernel.org>,
<kvm@vger.kernel.org>, <agraf@suse.de>,
Bharat Bhushan <Bharat.Bhushan@freescale.com>
Subject: Re: [PATCH 2/2 v5] KVM: PPC: booke: Add watchdog emulation
Date: Wed, 25 Jul 2012 18:55:16 -0500 [thread overview]
Message-ID: <50108764.2070906@freescale.com> (raw)
In-Reply-To: <20120725203708.GA31840@amt.cnet>
On 07/25/2012 03:37 PM, Marcelo Tosatti wrote:
> On Fri, Jul 20, 2012 at 04:29:08PM -0500, Scott Wood wrote:
>> On 07/20/2012 12:00 AM, Bharat Bhushan wrote:
>>> This patch adds the watchdog emulation in KVM. The watchdog
>>> emulation is enabled by KVM_ENABLE_CAP(KVM_CAP_PPC_WDT) ioctl.
>>> The kernel timer are used for watchdog emulation and emulates
>>> h/w watchdog state machine. On watchdog timer expiry, it exit to QEMU
>>> if TCR.WRC is non ZERO. QEMU can reset/shutdown etc depending upon how
>>> it is configured.
>
> Why can't you do this in QEMU, given the kernel exits to userspace on
> timer configuration?
>
> The QEMU timer handler used to emulate the watchdog then would have to
> only read the register value from the vCPU.
Do what specifically in QEMU? The whole watchdog mechanism?
It's only on final (third) expiry, when a reset is needed, that it exits
to QEMU. The first expiry sets a bit in TSR that software can clear to
clear the watchdog. If software doesn't clear it, the second expiry
sets a different bit in TSR that triggers a critical interrupt to the
guest. If software doesn't clear either of those bits by the time it
expires again, it's reset time (if a reset action is enabled).
The TSR/TCR registers are shared with other timers that are implemented
in the kernel, and it would be more complicated to implement just the
watchdog in QEMU. Plus, we currently have no interface for exiting to
QEMU for emulation of an SPR.
Currently QEMU on PPC leaves all timekeeping stuff to the kernel, and
I'd like to keep it that way.
-Scott
next prev parent reply other threads:[~2012-07-25 23:55 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-07-20 5:00 [PATCH 2/2 v5] KVM: PPC: booke: Add watchdog emulation Bharat Bhushan
2012-07-20 21:29 ` Scott Wood
2012-07-21 8:37 ` Bhushan Bharat-R65777
2012-07-23 15:35 ` Scott Wood
2012-07-23 4:10 ` Bhushan Bharat-R65777
2012-07-23 15:32 ` Scott Wood
2012-07-23 15:43 ` Bhushan Bharat-R65777
2012-07-23 16:00 ` Scott Wood
2012-07-23 16:04 ` Bhushan Bharat-R65777
2012-07-23 16:30 ` Scott Wood
2012-07-24 7:45 ` Bhushan Bharat-R65777
2012-07-24 22:32 ` Scott Wood
2012-07-25 20:37 ` Marcelo Tosatti
2012-07-25 23:55 ` Scott Wood [this message]
2012-07-26 0:46 ` Marcelo Tosatti
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