[Qemu-devel] [PATCH 03/27] Add a hook to allow hypercalls to be emulated on PowerPC

[David Gibson <david@gibson.dropbear.id.au>]

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 |    8 ++++++++
 2 files changed, 10 insertions(+), 0 deletions(-)

diff --git a/target-ppc/cpu.h b/target-ppc/cpu.h
index 124bbbf..36ca342 100644
--- a/target-ppc/cpu.h
+++ b/target-ppc/cpu.h
@@ -1646,4 +1646,6 @@ static inline void cpu_set_tls(CPUState *env, target_ulong newtls)
 #endif
 }
 
+extern void (*cpu_ppc_hypercall)(CPUState *);
+
 #endif /* !defined (__CPU_PPC_H__) */
diff --git a/target-ppc/helper.c b/target-ppc/helper.c
index 2094ca3..452a35c 100644
--- a/target-ppc/helper.c
+++ b/target-ppc/helper.c
@@ -70,6 +70,10 @@
 #  define LOG_EXCP(...) do { } while (0)
 #endif
 
+/*****************************************************************************/
+/* PowerPC Hypercall emulation */
+
+void (*cpu_ppc_hypercall)(CPUState *);
 
 /*****************************************************************************/
 /* PowerPC MMU emulation */
@@ -2152,6 +2156,10 @@ 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) && cpu_ppc_hypercall) {
+            cpu_ppc_hypercall(env);
+            return;
+        }
         if (lev == 1 || (lpes0 == 0 && lpes1 == 0))
             new_msr |= (target_ulong)MSR_HVB;
         goto store_next;
-- 
1.7.1