Re: [Xen-devel] [PATCH v4 2/9] xen/arm: Add more registers for saving and restoring vcpu registers

[Tim Deegan <tim@xxxxxxx>]

At 09:43 +0100 on 11 Oct (1381484614), Ian Campbell wrote:
> On Fri, 2013-10-11 at 17:30 +0900, Jaeyong Yoo wrote:
> > > -----Original Message-----
> > > From: xen-devel-bounces@xxxxxxxxxxxxx [mailto:xen-devel-
> > > bounces@xxxxxxxxxxxxx] On Behalf Of Ian Campbell
> > > Sent: Thursday, October 10, 2013 7:41 PM
> > > To: Jaeyong Yoo
> > > Cc: Tim Deegan; xen-devel@xxxxxxxxxxxxx
> > > Subject: Re: [Xen-devel] [PATCH v4 2/9] xen/arm: Add more registers for
> > > saving and restoring vcpu registers
> > > 
> > > On Fri, 2013-10-04 at 13:43 +0900, Jaeyong Yoo wrote:
> > > > diff --git a/xen/include/public/arch-arm.h
> > > > b/xen/include/public/arch-arm.h index 5d359af..bf6dc9a 100644
> > > > --- a/xen/include/public/arch-arm.h
> > > > +++ b/xen/include/public/arch-arm.h
> > > > @@ -253,6 +253,41 @@ struct vcpu_guest_context {
> > > >
> > > >      uint32_t sctlr, ttbcr;
> > > >      uint64_t ttbr0, ttbr1;
> > > > +    uint32_t ifar, dfar;
> > > > +    uint32_t ifsr, dfsr;
> > > > +    uint32_t dacr;
> > > > +    uint64_t par;
> > > > +
> > > > +#ifdef CONFIG_ARM_32
> > > 
> > > I'm afraid a per arch ifdef isn't allowed in the include/public tree.
> > > The interface should be identical for both 32 and 64 bit callers. Also
> > > think of 32-on-64 guests etc.
> > > 
> > > Also, this struct is guest facing (via VCPUOP_initialise) but many/all of
> > > these new registers are not things which a guest needs to specify via a
> > > hypercall. IOW I think many of them should be part of some toolstack
> > > private save/restore interface.
> > 
> > I see, the guest can specify something like sctlr, and ttbr/ttbcr, and the
> > others should be hidden inside hvm save/restore. 
> 
> Right, the important thing is that all that additional state is only
> visible to the toolstack and the hypervisor, not to guests.
> 
> Actually the guest shouldn't really see this interface anyway, that's
> really a hold over from x86. On ARM only the toolstack really needs to
> use this struct.
> 
> I wonder if we can drop struct vcpu_guest_context from the guest facing
> ABI on ARM. I see that we already don't expose VCPUOP_initialise and the
> only other user is XEN_DOMCTL_(sg)etvcpucontext.

Does the guest need to have those on ARM? How are you arranging SMP
guest AP bringup?  If it's using SCI then maybe that hypercall interface
can be dropped.

Tim.

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