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 -- 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
