Re: RFC: proposal for VM reset & shutdown hcall (v2)

[Alexander Graf <agraf@suse.de>]

On 07/02/2013 05:07 PM, Yoder Stuart-B08248 wrote:
> Version 2 changes
>     -remove advertising via KVM_HC_FEATURES
>     -define a new exit type (KVM_EXIT_EPAPR_HCALL) for user space
>      handled hcalls
>     -advertise KVM_EXIT_EPAPR_HCALL to user space via new capability
>      flag
>     -defined device tree properties to advertise the existence
>      of reset and shutdown hcalls to a guest
>
> ------------------------------------------------------------------------
> KVM_CAP_EXIT_EPAPR_HCALL  Capability
>
> A new capability KVM_CAP_EXIT_EPAPR_HCALL is defined to advertise
> the new KVM_EXIT_EPAPR_HCALL exit .
>
> ------------------------------------------------------------------------
> KVM_EXIT_EPAPR_HCALL exit definition
>
>                  /* KVM_EXIT_EPAPR_HCALL */
>                  struct {
>                          __u64 nr;
>                          __u64 ret;
>                          __u64 args[8];
>                  } epapr_hcall;
>
> This is used on e500 Power Architecture for the paravirt e500

It can also be used on book3s systems. We use the same logic for -M 
g3beige and -M mac99. We even use it for -M mpc8544ds.

> platform.  It occurs when a guest does a hypercall (as defined
> in the ePAPR 1.1) and the hcall is not handled by the kernel.
>
> The 'nr' field contains the hypercall number (from the guest R11),
> and 'args' contains the arguments (from the guest R3 - R10).
> Userspace should put the return code in 'ret' and any extra returned
> values in args[].

Please specify which registers ret and args will end up in.

>
> ------------------------------------------------------------------------
> Advertising reset and shutdown in device tree.
>
> A virtual machine can detect the availability of the reset
> and shutdown hcalls by looking at properties on the /hypervisor
> node.
>
>      Property name: has-reset

I don't remember how ePAPR specifies this. Aren't keys in /hypervisor 
supposed to be common throughout hypervisors? So if Windriver wants to 
add a reset hypercall, they'd also add "has-reset"? How does the guest 
know which hcall number to issue?

Thanks a lot for writing all of this down :)

Alex

>      Value type:<none>
>      Definition:  If the property is present the hypervisor supports
>                   the KVM_HC_VM_RESET hcall.
>
>      Property name: has-shutdown
>      Value type:<none>
>      Definition:  If the property is present the hypervisor supports
>                   the KVM_HC_VM_SHUTDOWN hcall.
>
> ------------------------------------------------------------------------
> Hypercall: KVM_HC_VM_RESET
> Description:  Requests that the virtual machine be reset.  The
>                hcall takes no arguments. If successful the hcall does not
>                return.
>
> Arguments:
>       r11    hcall-token   KVM_HC_VM_RESET
>
> Return values
>       r3     status        Status of the hcall.  If the hcall succeeds
>                            it does not return.  If an error occurs
>                            EV_INTERNAL is returned.
>
> ------------------------------------------------------------------------
> Hypercall: KVM_HC_VM_SHUTDOWN
> Description:  Requests that the virtual machine be powered-off/halted.
>                The hcall takes no arguments. If successful the hcall does not
>                return.
>
> Arguments:
>       r11    hcall-token   KVM_HC_VM_SHUTDOWN
>
> Return values
>       r3     status        Status of the hcall.  If the hcall succeeds
>                            it does not return.  If an error occurs
>                            EV_INTERNAL is returned.
>
>
>
> Regards,
> Stuart
>
>