[Xen-devel] [PATCH-RESEND] Disable MCE if MCE banks are not present

["Aravindh Puthiyaparambil (aravindp)" <aravindp@xxxxxxxxx>]

(My previous email had extra line breaks. Hopefully this one does not. I have 
also included the patch as an attachement.)
Do not continue with machine check setup if MCE banks are not present. This 
fixes Xen boot on VMware hypervisors.

When booting Xen on VMware ESX 5.1 and Workstation 9, you hit a GPF during MCE 
initialization. The culprit is line 631 in set_poll_bankmask():
                bitmap_copy(mb->bank_map, mca_allbanks->bank_map, nr_mce_banks);

What is happening is that in mca_cap_init(), nr_mce_banks is being set to 0. 
This causes the allocation of bank_map to be set to ZERO_BLOCK_PTR which is the 
return value for zero-size allocation by xzalloc_array()/_xmalloc(). This 
results in the bitmap_copy() to fail disastrously. The following patch fixes 
this issue.

Signed-off-by: Aravindh Puthiyaparambil <aravindp@xxxxxxxxx>

diff --git a/xen/arch/x86/cpu/mcheck/mce.c b/xen/arch/x86/cpu/mcheck/mce.c
index 6712db1..9cbd4aa 100644
--- a/xen/arch/x86/cpu/mcheck/mce.c
+++ b/xen/arch/x86/cpu/mcheck/mce.c
@@ -652,7 +652,14 @@ int mca_cap_init(void)
     }
     nr_mce_banks = msr_content & MCG_CAP_COUNT;

-    /* mcabanks_alloc depends on nr_mcebanks */
+    if (!nr_mce_banks)
+    {
+        printk(XENLOG_INFO "CPU%i: No MCE banks present. "
+               "Machine check support disabled\n", smp_processor_id());
+        return -ENODEV;
+    }
+
+    /* mcabanks_alloc depends on nr_mce_banks */
     if (!mca_allbanks)
     {
         int i;

Attachment: mce_nobanks_disable.patch
Description: mce_nobanks_disable.patch

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