Re: [Qemu-devel] [PATCH 03/26] Add a hook to allow hypercalls to be emulated on PowerPC

[Anthony Liguori <anthony@codemonkey.ws>]

On 03/15/2011 11:56 PM, David Gibson wrote:
> From: David Gibson<dwg@au1.ibm.com>
>
> PowerPC and POWER chips since the POWER4 and 970 have a special
> hypervisor mode, and a corresponding form of the system call
> instruction which traps to the hypervisor.
>
> qemu currently has stub implementations of hypervisor mode.  That
> is, the outline is there to allow qemu to run a PowerPC hypervisor
> under emulation.  There are a number of details missing so this
> won't actually work at present, but the idea is there.
>
> What there is no provision at all, is for qemu to instead emulate
> the hypervisor itself.  That is to have hypercalls trap into qemu
> and their result be emulated from qemu, rather than running
> hypervisor code within the emulated system.
>
> Hypervisor hardware aware KVM implementations are in the works and
> it would  be useful for debugging and development to also allow
> full emulation of the same para-virtualized guests as such a KVM.
>
> Therefore, this patch adds a hook which will allow a machine to
> set up emulation of hypervisor calls.
>
> Signed-off-by: David Gibson<dwg@au1.ibm.com>
> ---
>   target-ppc/cpu.h    |    2 ++
>   target-ppc/helper.c |    4 ++++
>   2 files changed, 6 insertions(+), 0 deletions(-)
>
> diff --git a/target-ppc/cpu.h b/target-ppc/cpu.h
> index a20c132..eaddc27 100644
> --- a/target-ppc/cpu.h
> +++ b/target-ppc/cpu.h
> @@ -692,6 +692,8 @@ struct CPUPPCState {
>       int bfd_mach;
>       uint32_t flags;
>       uint64_t insns_flags;
> +    void (*emulate_hypercall)(CPUState *, void *);
> +    void *hcall_opaque;

Is the hypercall handler ever specific to a CPU?

I'd prefer to see this as a generic interface that wasn't specific to 
target-ppc.

Basically, add a:

void cpu_hypercall(CPUState *env);

And then implement it within your target.  I'm not sure I get the opaque 
argument.

Regards,

Anthony Liguori

>
>       int error_code;
>       uint32_t pending_interrupts;
> diff --git a/target-ppc/helper.c b/target-ppc/helper.c
> index 2094ca3..19aa067 100644
> --- a/target-ppc/helper.c
> +++ b/target-ppc/helper.c
> @@ -2152,6 +2152,10 @@ static inline void powerpc_excp(CPUState *env, int excp_model, int excp)
>       case POWERPC_EXCP_SYSCALL:   /* System call exception                    */
>           dump_syscall(env);
>           lev = env->error_code;
> +	if ((lev == 1)&&  env->emulate_hypercall) {
> +	    env->emulate_hypercall(env, env->hcall_opaque);
> +	    return;
> +	}	
>           if (lev == 1 || (lpes0 == 0&&  lpes1 == 0))
>               new_msr |= (target_ulong)MSR_HVB;
>           goto store_next;