Re: [PATCH 3/5] booke: define reset and shutdown hcalls

[Scott Wood <scottwood@freescale.com>]

On 07/15/2013 06:30:20 AM, Gleb Natapov wrote:
> On Mon, Jul 15, 2013 at 04:41:17PM +0530, Bharat Bhushan wrote:
> > KVM_HC_VM_RESET: Requests that the virtual machine be reset.
> > KVM_HC_VM_SHUTDOWN: Requests that the virtual machine be  
> powered-off/halted.
> >
> > These hcalls are handled by guest userspace.
> >
> > Signed-off-by: Bharat Bhushan <bharat.bhushan@freescale.com>
> > ---
> >  Documentation/virtual/kvm/hypercalls.txt |   16 ++++++++++++++++
> >  include/uapi/linux/kvm_para.h            |    3 ++-
> >  2 files changed, 18 insertions(+), 1 deletions(-)
> >
> > diff --git a/Documentation/virtual/kvm/hypercalls.txt  
> b/Documentation/virtual/kvm/hypercalls.txt
> > index ea113b5..58acdc1 100644
> > --- a/Documentation/virtual/kvm/hypercalls.txt
> > +++ b/Documentation/virtual/kvm/hypercalls.txt
> > @@ -64,3 +64,19 @@ Purpose: To enable communication between the  
> hypervisor and guest there is a
> >  shared page that contains parts of supervisor visible register  
> state.
> >  The guest can map this shared page to access its supervisor  
> register through
> >  memory using this hypercall.
> > +
> > +5. KVM_HC_VM_RESET
> > +------------------------
> > +Architecture: PPC
> > +Status: active
> > +Purpose:  Requests that the virtual machine be reset.  The hcall  
> takes no
> > +arguments. If successful the hcall does not return. If an error  
> occurs it
> > +returns EV_INTERNAL.
> > +
> > +6. KVM_HC_VM_SHUTDOWN
> > +------------------------
> > +Architecture: PPC
> > +Status: active
> > +Purpose: Requests that the virtual machine be powered-off/halted.
> > +The hcall takes no arguments. If successful the hcall does not  
> return.
> > +If an error occurs it returns EV_INTERNAL.
> > diff --git a/include/uapi/linux/kvm_para.h  
> b/include/uapi/linux/kvm_para.h
> > index cea2c5c..218882d 100644
> > --- a/include/uapi/linux/kvm_para.h
> > +++ b/include/uapi/linux/kvm_para.h
> > @@ -19,7 +19,8 @@
> >  #define KVM_HC_MMU_OP			2
> >  #define KVM_HC_FEATURES			3
> >  #define KVM_HC_PPC_MAP_MAGIC_PAGE	4
> > -
> > +#define KVM_HC_VM_RESET			5
> > +#define KVM_HC_VM_SHUTDOWN		6
> There is no much sense to share hypercalls between architectures.  
> There
> is zero probability x86 will implement those for instance

This is similar to the question of whether to keep device API  
enumerations per-architecture...  It costs very little to keep it in a  
common place, and it's hard to go back in the other direction if we  
later realize there are things that should be shared.

Keeping it in a common place also makes it more visible to people  
looking to add new hcalls, which could cut down on reinventing the  
wheel.

> (not sure why PPC will want them either instead of emulating devices  
> that do
> shutdown/reset).

Besides what Alex said, for shutdown we don't have any existing device  
to emulate (our real hardware just doesn't have that functionality).   
For reset we currently do emulate, but it's awkward to describe in the  
device tree what we actually emulate since the reset functionality is  
part of a kitchen-sink "device" of which we emulate virtually nothing  
other than the reset.  Currently we advertise the entire thing and just  
ignore the rest, but that causes problems with the guest seeing the  
node and trying to use that functionality.

-Scott