Dump machine check context for fatal machine check

This small patches enable Xen hypervisor to always dump machine check
ontext, previously it will not print anything if fatal MCE happens. It
also add checking for NULL pointer.

It also change the address passing to guest to always use guest
mfn. It should benifit non-translated guest.

Signed-off-by: Jiang, Yunhong <yunhong.jiang@intel.com>

xen/arch/x86/cpu/mcheck/mce_intel.c

@@ -370,7 +370,7 @@ static void intel_UCR_handler(struct mcinfo_bank *bank,
                           }
 
                           gfn =
-                              mfn_to_gmfn(d, ((bank->mc_addr) >> PAGE_SHIFT));
+                              get_gpfn_from_mfn((bank->mc_addr) >> PAGE_SHIFT);
                           bank->mc_addr =  gfn << PAGE_SHIFT |
                                         (bank->mc_addr & (PAGE_SIZE -1 ));
                           if (fill_vmsr_data(bank, global->mc_gstatus) == -1)
@@ -663,6 +663,10 @@ static void intel_machine_check(struct cpu_user_regs * regs, long error_code)
     mctc = mcheck_mca_logout(MCA_MCE_SCAN, mca_allbanks, &bs, &clear_bank);
 
     if (bs.errcnt) {
+        /* dump MCE error */
+        if (mctc != NULL)
+            x86_mcinfo_dump(mctelem_dataptr(mctc));
+
         /*
          * Uncorrected errors must be dealth with in softirq context.
          */
@@ -690,9 +694,6 @@ static void intel_machine_check(struct cpu_user_regs * regs, long error_code)
         mce_printk(MCE_CRITICAL, "MCE: clear_bank map %lx on CPU%d\n",
                 *((unsigned long*)clear_bank), smp_processor_id());
         mcheck_mca_clearbanks(clear_bank);
-       /* Print MCE error */
-        x86_mcinfo_dump(mctelem_dataptr(mctc));
-
     } else {
         if (mctc != NULL)
             mctelem_dismiss(mctc);