[Xen-devel] [PATCH V2] x86, amd_ucode: Skip microcode updates for final levels

[Aravind Gopalakrishnan <aravind.gopalakrishnan@xxxxxxx>]

Some of older[Fam10h] systems require that certain number of
applied microcode patch levels should not be overwritten by
the microcode loader. Otherwise, system hangs are known to occur.

The 'final_levels' of patch ids have been obtained empirically.
Refer bug https://bugzilla.suse.com/show_bug.cgi?id=913996
for details of the issue.

The short version is that people have predominantly noticed
system hang issues when trying to update microcode levels
beyond the patch IDs below.
[0x01000098, 0x0100009f, 0x010000af]

From internal discussions, we gathered that OS/hypervisor
cannot reliably perform microcode updates beyond these levels
due to hardware issues. Therefore, we need to abort microcode
update process if we hit any of these levels.

In this patch, we check for those microcode versions and abort
if the current core has one of those final patch levels applied
by the BIOS

A linux version of the patch has already made it into tip-
http://marc.info/?l=linux-kernel&m=143703405627170

Signed-off-by: Aravind Gopalakrishnan <aravind.gopalakrishnan@xxxxxxx>
---
Changes from V1 (per Andrew)
  - use commit text from linux patch
  - include details about how 'final_levels' are obtaines in comments
    (I have also copied it into commit message. But shall remove if you
     feel it's redundant)
  - use ARRAY_SIZE() and kill NULL terminator
  - use XENLOG_INFO in place of pr_debug()
  - correct unsigned int usage

 xen/arch/x86/microcode_amd.c | 42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/xen/arch/x86/microcode_amd.c b/xen/arch/x86/microcode_amd.c
index f79b397..a9761dc 100644
--- a/xen/arch/x86/microcode_amd.c
+++ b/xen/arch/x86/microcode_amd.c
@@ -347,6 +347,40 @@ static int container_fast_forward(const void *data, size_t 
size_left, size_t *of
     return 0;
 }
 
+/*
+ * The 'final_levels' of patch ids have been obtained empirically.
+ * Refer bug https://bugzilla.suse.com/show_bug.cgi?id=913996
+ * for details of the issue. The short version is that people
+ * have predominantly noticed system hang issues when trying to
+ * update microcode levels beyond the patch IDs below.
+ * From internal discussions, we gathered that OS/hypervisor
+ * cannot reliably perform microcode updates beyond these levels
+ * due to hardware issues. Therefore, we need to abort microcode
+ * update process if we hit any of these levels.
+ */
+static unsigned int final_levels[] = {
+    0x01000098,
+    0x0100009f,
+    0x010000af
+};
+
+static bool_t check_final_patch_levels(int cpu)
+{
+    /*
+     * Check the current patch levels on the cpu. If they are equal to
+     * any of the 'final_levels', then we should not update the microcode
+     * patch on the cpu as system will hang otherwise.
+     */
+    struct ucode_cpu_info *uci = &per_cpu(ucode_cpu_info, cpu);
+    unsigned int i;
+
+    for ( i = 0; i < ARRAY_SIZE(final_levels); i++ )
+        if ( uci->cpu_sig.rev == final_levels[i] )
+            return 1;
+
+    return 0;
+}
+
 static int cpu_request_microcode(int cpu, const void *buf, size_t bufsize)
 {
     struct microcode_amd *mc_amd, *mc_old;
@@ -369,6 +403,14 @@ static int cpu_request_microcode(int cpu, const void *buf, 
size_t bufsize)
         goto out;
     }
 
+    if ( check_final_patch_levels(cpu) )
+    {
+        printk(XENLOG_INFO
+               "microcode: Cannot update microcode patch on the cpu as we hit 
a final level\n");
+        error = -EPERM;
+        goto out;
+    }
+
     mc_amd = xmalloc(struct microcode_amd);
     if ( !mc_amd )
     {
-- 
1.9.1


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