From: Marcelo Tosatti <mtosatti@redhat.com>
To: Scott Wood <scottwood@freescale.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 21:46:43 -0300 [thread overview]
Message-ID: <20120726004643.GA3904@amt.cnet> (raw)
In-Reply-To: <50108764.2070906@freescale.com>
On Wed, Jul 25, 2012 at 06:55:16PM -0500, Scott Wood wrote:
> 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
>
OK.
prev parent reply other threads:[~2012-07-26 0:46 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
2012-07-26 0:46 ` Marcelo Tosatti [this message]
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