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

From: Anthony Liguori
Subject: Re: [Qemu-devel] [PATCH 03/26] Add a hook to allow hypercalls to be emulated on PowerPC
Date: Wed, 16 Mar 2011 15:44:49 -0500
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On 03/15/2011 11:56 PM, David Gibson wrote:
From: David Gibson<address@hidden>

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<address@hidden>
  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.


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                    
          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;

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