x86/hvm: improve "Emulation failed @" error messages

* Introduce hvm_dump_emulation_state() to be a common implementation rather
  than having the printk() open-coded slightly differently in 3 separate
  places.
* Identify the vcpu operating mode to allow for unambiguous decoding of the
  instruction bytes.
* A valid instruction can be up to 15 bytes long, but may also be shorter than
  the current arbitrary 10 bytes.  Print only the fetched bytes, which could
  include nothing if the emulation failed due to an inability to fetch the
  instruction.

A sample new error message looks like:

(d1) MMIO emulation failed: d1v0 64bit @ 0008:ffff82d0802c4f20 -> 48 8b b8 e8 7f 00 00

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Tim Deegan <tim@xen.org>
Release-acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>

xen/arch/x86/hvm/emulate.c

@@ -1420,15 +1420,7 @@ void hvm_mem_event_emulate_one(bool_t nowrite, unsigned int trapnr,
          */
         return;
     case X86EMUL_UNHANDLEABLE:
-        gdprintk(XENLOG_DEBUG, "Emulation failed @ %04x:%lx: "
-               "%02x %02x %02x %02x %02x %02x %02x %02x %02x %02x\n",
-               hvmemul_get_seg_reg(x86_seg_cs, &ctx)->sel,
-               ctx.insn_buf_eip,
-               ctx.insn_buf[0], ctx.insn_buf[1],
-               ctx.insn_buf[2], ctx.insn_buf[3],
-               ctx.insn_buf[4], ctx.insn_buf[5],
-               ctx.insn_buf[6], ctx.insn_buf[7],
-               ctx.insn_buf[8], ctx.insn_buf[9]);
+        hvm_dump_emulation_state(XENLOG_G_DEBUG "Mem event", &ctx);
         hvm_inject_hw_exception(trapnr, errcode);
         break;
     case X86EMUL_EXCEPTION:
@@ -1479,6 +1471,32 @@ struct segment_register *hvmemul_get_seg_reg(
     return &hvmemul_ctxt->seg_reg[seg];
 }
 
+static const char *guest_x86_mode_to_str(int mode)
+{
+    switch ( mode )
+    {
+    case 0:  return "Real";
+    case 1:  return "v86";
+    case 2:  return "16bit";
+    case 4:  return "32bit";
+    case 8:  return "64bit";
+    default: return "Unknown";
+    }
+}
+
+void hvm_dump_emulation_state(const char *prefix,
+                              struct hvm_emulate_ctxt *hvmemul_ctxt)
+{
+    struct vcpu *curr = current;
+    const char *mode_str = guest_x86_mode_to_str(hvm_guest_x86_mode(curr));
+    const struct segment_register *cs =
+        hvmemul_get_seg_reg(x86_seg_cs, hvmemul_ctxt);
+
+    printk("%s emulation failed: %pv %s @ %04x:%08lx -> %*ph\n",
+           prefix, curr, mode_str, cs->sel, hvmemul_ctxt->insn_buf_eip,
+           hvmemul_ctxt->insn_buf_bytes, hvmemul_ctxt->insn_buf);
+}
+
 /*
  * Local variables:
  * mode: C

xen/arch/x86/hvm/io.c

@@ -100,16 +100,7 @@ int handle_mmio(void)
     switch ( rc )
     {
     case X86EMUL_UNHANDLEABLE:
-        gdprintk(XENLOG_WARNING,
-                 "MMIO emulation failed @ %04x:%lx: "
-                 "%02x %02x %02x %02x %02x %02x %02x %02x %02x %02x\n",
-                 hvmemul_get_seg_reg(x86_seg_cs, &ctxt)->sel,
-                 ctxt.insn_buf_eip,
-                 ctxt.insn_buf[0], ctxt.insn_buf[1],
-                 ctxt.insn_buf[2], ctxt.insn_buf[3],
-                 ctxt.insn_buf[4], ctxt.insn_buf[5],
-                 ctxt.insn_buf[6], ctxt.insn_buf[7],
-                 ctxt.insn_buf[8], ctxt.insn_buf[9]);
+        hvm_dump_emulation_state(XENLOG_G_WARNING "MMIO", &ctxt);
         return 0;
     case X86EMUL_EXCEPTION:
         if ( ctxt.exn_pending )

xen/arch/x86/hvm/vmx/realmode.c

@@ -157,14 +157,7 @@ static void realmode_emulate_one(struct hvm_emulate_ctxt *hvmemul_ctxt)
     return;
 
  fail:
-    gdprintk(XENLOG_ERR,
-             "Real-mode emulation failed @ %04x:%08lx: "
-             "%02x %02x %02x %02x %02x %02x\n",
-             hvmemul_get_seg_reg(x86_seg_cs, hvmemul_ctxt)->sel,
-             hvmemul_ctxt->insn_buf_eip,
-             hvmemul_ctxt->insn_buf[0], hvmemul_ctxt->insn_buf[1],
-             hvmemul_ctxt->insn_buf[2], hvmemul_ctxt->insn_buf[3],
-             hvmemul_ctxt->insn_buf[4], hvmemul_ctxt->insn_buf[5]);
+    hvm_dump_emulation_state(XENLOG_G_ERR "Real-mode", hvmemul_ctxt);
     domain_crash(curr->domain);
 }
 

xen/include/asm-x86/hvm/emulate.h

@@ -54,4 +54,7 @@ int hvmemul_do_pio(
     unsigned long port, unsigned long *reps, int size,
     paddr_t ram_gpa, int dir, int df, void *p_data);
 
+void hvm_dump_emulation_state(const char *prefix,
+                              struct hvm_emulate_ctxt *hvmemul_ctxt);
+
 #endif /* __ASM_X86_HVM_EMULATE_H__ */