Re: [PATCH] cpu: Add starts_halted() method

[Greg Kurz]

On Thu, 9 Jul 2020 14:21:04 +0200
Philippe Mathieu-Daudé <philmd@redhat.com> wrote:

> On 7/9/20 12:55 PM, Greg Kurz wrote:
> > On Thu, 9 Jul 2020 12:18:06 +0200
> > Philippe Mathieu-Daudé <philmd@redhat.com> wrote:
> >

[...]

> >>>
> >>> FYI, PAPR requires all vCPUs to be "stopped" by default. It is up to the
> >>> guest to start them explicitly through an RTAS call. The hypervisor is
> >>> only responsible to start a single vCPU (see spapr_cpu_set_entry_state()
> >>> called from spapr_machine_reset()) to be able to boot the guest.
> >>>
> >>> So I'm not sure to see how that would depend on the accelerator...
> >>
> >> $ qemu-system-ppc64 -M pseries-5.0,accel=tcg -d in_asm
> >> qemu-system-ppc64: warning: TCG doesn't support requested feature,
> >> cap-cfpc=workaround
> >> qemu-system-ppc64: warning: TCG doesn't support requested feature,
> >> cap-sbbc=workaround
> >> qemu-system-ppc64: warning: TCG doesn't support requested feature,
> >> cap-ibs=workaround
> >> qemu-system-ppc64: warning: TCG doesn't support requested feature,
> >> cap-ccf-assist=on
> >> ----------------
> >> IN:
> >> 0x00000100:  48003f00  b        0x4000
> >>
> >> ----------------
> >> IN:
> >> 0x00004000:  7c7f1b78  mr       r31, r3
> >> 0x00004004:  7d6000a6  mfmsr    r11
> >> 0x00004008:  3980a000  li       r12, 0xa000
> >> 0x0000400c:  798c83c6  sldi     r12, r12, 0x30
> >> 0x00004010:  7d6b6378  or       r11, r11, r12
> >> 0x00004014:  7d600164  mtmsrd   r11
> >> ...
> >>
> >> The vCPU doesn't seem stopped to me...
> >>
> >> Am I missing something?
> >>
> > 
> > Yeah this is the boot vCPU which is required to be started
> > by the platform as explained above, but if you had more
> > vCPUs the other ones would be stopped until the guest OS
> > asks us to start them.
> 
> Ah OK, so we are good :)
> 
> The machine simply has to set the 'start-powered-off' flag on
> all vCPUS except the 1st one.
> 

We only want the first vCPU to start when the platform is
fully configured, so I'd rather put 'start-powered-off' on
every body and explicitly power on the first one during
machine reset as we do now.