[RFC PATCH 2/2] ARM: SMP support for mach-virt

[Stefano Stabellini]

On Tue, 4 Dec 2012, Will Deacon wrote:
> On Tue, Dec 04, 2012 at 05:24:57PM +0000, Marc Zyngier wrote:
> > On 04/12/12 17:16, Will Deacon wrote:
> > > On Tue, Dec 04, 2012 at 04:45:58PM +0000, Rob Herring wrote:
> > >> Aren't we mixing 2 pens here? You must have some simple bootloader
> > >> containing vector table and a pen that the dtb points to, right? The pen
> > >> you have in the kernel is only needed when hotplug only does a wfi. As
> > >> you don't yet support hotplug, then you can drop all the kernel pen code.
> > > 
> > > Yes, both qemu and kvmtool have bootloader pens outside of the kernel but
> > > since wfi is not trapped by kvm, the secondaries can be released early due
> > > to a spurious wakeup so we need the second pen.
> > 
> > Actually, KVM traps WFI and puts the vcpu thread on a wait queue (we are
> > actually giving more guaranties than the architecture offers here).
> 
> Ok, if we can rely on this behaviour in the future this sounds promising.
> Can somebody comment from the Xen side of things please?

Hi!
Sorry for taking so long to reply but I admit I missed the thread
entirely until now. I would appreciate if you could CC
xen-devel at lists.xen.org and/or me for virtualization related
discussions.

On the Xen side there are not going to be any problems related to SMP
and holding pens, because secondary CPUs only come into existence after
the first CPU calls the HYPERVISOR_vcpu_op hypercall (still missing on
ARM).