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. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
