icount: update instruction counter on apic patching

kvmvapic patches the code when some instructions are executed.
E.g. mov 0xff, 0xfffe0080 is interpreted as push 0xff/call ...
This patching is also followed by some side effects (changing apic
and guest memory state). Therefore deterministic execution should take
this operation into account. This patch decreases icount when original
mov instruction is trying to execute. Therefore patching becomes
deterministic and can be replayed correctly.

Signed-off-by: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>
Message-Id: <20170124071702.4572.17294.stgit@PASHA-ISP>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/hw/i386/kvmvapic.c b/hw/i386/kvmvapic.c
index 702e281..7135633 100644
--- a/hw/i386/kvmvapic.c
+++ b/hw/i386/kvmvapic.c
@@ -413,6 +413,12 @@ static void patch_instruction(VAPICROMState *s, X86CPU *cpu, target_ulong ip)
     if (!kvm_enabled()) {
         cpu_get_tb_cpu_state(env, &current_pc, &current_cs_base,
                              &current_flags);
+        /* Account this instruction, because we will exit the tb.
+           This is the first instruction in the block. Therefore
+           there is no need in restoring CPU state. */
+        if (use_icount) {
+            --cs->icount_decr.u16.low;
+        }
     }
 
     pause_all_vcpus();