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

[Jaeyong Yoo <jaeyong.yoo@xxxxxxxxxxx>]

> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxx [mailto:xen-devel-
> bounces@xxxxxxxxxxxxx] On Behalf Of Jaeyong Yoo
> Sent: Monday, October 14, 2013 1:39 PM
> To: 'Ian Campbell'; 'Tim Deegan'
> Cc: 'Stefano Stabellini'; 'Keir Fraser'; 'Jan Beulich'; xen-
> devel@xxxxxxxxxxxxx
> Subject: Re: [Xen-devel] [PATCH v4 2/9] xen/arm: Add more registers for
> saving and restoring vcpu registers
> 
> > -----Original Message-----
> > From: xen-devel-bounces@xxxxxxxxxxxxx [mailto:xen-devel-
> > bounces@xxxxxxxxxxxxx] On Behalf Of Ian Campbell
> > Sent: Friday, October 11, 2013 7:26 PM
> > To: Tim Deegan
> > Cc: Keir Fraser; Stefano Stabellini; Jan Beulich; Jaeyong Yoo; xen-
> > devel@xxxxxxxxxxxxx
> > Subject: Re: [Xen-devel] [PATCH v4 2/9] xen/arm: Add more registers
> > for saving and restoring vcpu registers
> >
> > On Fri, 2013-10-11 at 11:22 +0100, Tim Deegan wrote:
> > > 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.
> >
> > SMP bring up is done via PSCI, which is the firmware "hypercall"
> > interface, defined by ARM for bringing up physucal CPUs which we
> > implement within Xen for the guests' benefit.
> 
> So, could I remove XEN_DOMCTL_(sg)etvcpucontext and use HVM save/restore
> for migrating vcpu registers?
> 
> And, if I could, arch_get_info_guest becomes dangling function and would
> it be better to remove this function too? or better to keep it for
> symmetry?

Are these questions missed?

> 
> Jaeyong
> 
> >
> > Ian
> >
> >
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxx
> > http://lists.xen.org/xen-devel
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxx
> http://lists.xen.org/xen-devel


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel