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

[Aravind Gopalakrishnan <aravind.gopalakrishnan@xxxxxxx>]

Some of older[Fam10h] systems require that the microcode versions
that it comes up with should not be updated by the microcode driver.
Otherwise, system hangs are known to occur.

In this patch, we check for those microcode versions and abort the
update process if existing microcode level is already 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>
---
 xen/arch/x86/microcode_amd.c | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/xen/arch/x86/microcode_amd.c b/xen/arch/x86/microcode_amd.c
index f79b397..c958a47 100644
--- a/xen/arch/x86/microcode_amd.c
+++ b/xen/arch/x86/microcode_amd.c
@@ -347,6 +347,30 @@ static int container_fast_forward(const void *data, size_t 
size_left, size_t *of
     return 0;
 }
 
+static unsigned int final_levels[] = {
+    0x01000098,
+    0x0100009f,
+    0x010000af,
+    0
+};
+
+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);
+    int i;
+
+    for ( i = 0; final_levels[i]; 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 +393,13 @@ static int cpu_request_microcode(int cpu, const void *buf, 
size_t bufsize)
         goto out;
     }
 
+    if ( check_final_patch_levels(cpu) )
+    {
+        pr_debug("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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