Re: [Patch][RFC] fix PAL_HALT ( is Re: [Xen-ia64-devel] [RFC] dump core is failed for PAL_HALT)

[Tristan Gingold <tgingold@xxxxxxx>]

On Wed, Jan 24, 2007 at 09:19:09AM -0700, Alex Williamson wrote:
> On Wed, 2007-01-24 at 11:14 +0100, tgingold@xxxxxxx wrote:
> > Selon Isaku Yamahata <yamahata@xxxxxxxxxxxxx>:
> > 
> > > On Wed, Jan 24, 2007 at 11:43:37AM +0900, Akio Takebe wrote:
> > [...]
> > > According to SDM vol2 11.9, PAL_HALT places cpu in low power state.
> > Correct.
> > 
> > > So the current behaviour that xen/ia64 shutdown unconditionally is
> > > wrong.
> > Yes, but that's the code in linux/ia64.
> > Why linux/ia64 doesn't call the shutdown EFI runtime service ?  I don't 
> > know.
> > Maybe Alex knows the answer.
> 
>    I think we need to be sure we're getting the correct expected user
> behavior for domains.  A user expects the following on real hardware:
> 
>       * halt: Machine is stopped, not shutdown, not rebooted.
>         Linux/ia64 uses PAL_HALT for this.
>       * restart/reboot: Machine is reset.  Linux/ia64 uses
>         efi.reset_system for this.
>       * poweroff: Machine is turned off.  Linux/ia64 uses ACPI S5 power
>         state if pm_power_off is set, otherwise behaves as if halted.
> 
> So, for PV domains, cpu_halt() should just take the vcpu offline.  I
> don't think there's any reason to special case the last vcpu going
> offline and shutdown the domain.  That's not what real hardware does.
Thanks for the details.  So current Xen/ia64 PAL_HALT behavior is not
correct.

> Machine restart/reboot should (and does) happen transparently when Xen
> catches the EFI call.  To support poweroff, I think we should set
> pm_power_off to a Xen specific hypervisor shutdown routine.  The
> abstraction is already in place to do this.
> 
> Do VTI domains implement enough ACPI to provide the OS a fake S5 power
> state?  If not, a PV-on-HVM driver could set pm_power_off and use a
> hypercall, but that means HVM domains would need a Xen driver for some
> pretty basic functionality.  Maybe all vcpus in cpu_halt() should only
> be cause for a domain shutdown for VTI domains?
I think VTI support S5, if not it should :-)

[...]
Tristan.

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