[PATCH] x86/ucode: Work around Granite Rapids erraturm GNR98

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Block loads which are known to hang the system.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <jbeulich@xxxxxxxx>
CC: Roger Pau Monné <roger@xxxxxxxxxxxxxx>
CC: Teddy Astie <teddy.astie@xxxxxxxxxx>

A more complete solution is in the works, but it's taken 4 months to get this
much published...
---
 xen/arch/x86/cpu/microcode/intel.c | 31 ++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/xen/arch/x86/cpu/microcode/intel.c 
b/xen/arch/x86/cpu/microcode/intel.c
index c45b00c6b033..2160befd3197 100644
--- a/xen/arch/x86/cpu/microcode/intel.c
+++ b/xen/arch/x86/cpu/microcode/intel.c
@@ -27,6 +27,7 @@
 #include <xen/string.h>
 #include <xen/xmalloc.h>
 
+#include <asm/intel-family.h>
 #include <asm/msr.h>
 #include <asm/processor.h>
 #include <asm/system.h>
@@ -273,6 +274,35 @@ static bool microcode_fits_cpu(const struct 
microcode_patch *mc)
     return false;
 }
 
+static bool microcode_safe_to_load(const struct microcode_patch *mc)
+{
+    struct cpu_signature *cpu_sig = &this_cpu(cpu_sig);
+
+    /*
+     * Treat pre-production as always safe - anyone using pre-production
+     * microcode knows what they are doing, and can keep any resulting pieces.
+     */
+    if ( cpu_sig->rev < 0 || mc->rev < 0 )
+        return true;
+
+    /*
+     * GNR98.  Granite Rapids systems hang when loading new ucode on
+     * sufficiently old firmware.
+     */
+    if ( boot_cpu_data.vfm == INTEL_GRANITERAPIDS_X &&
+         boot_cpu_data.stepping == 1 && (cpu_sig->pf & 0x95) &&
+         cpu_sig->rev < 0x01000405 &&
+         mc->rev      > 0x01000405 )
+    {
+        printk_once(XENLOG_WARNING
+                    "microcode: Granite Rapids erratum GNR98 detected.  
Skipping ucode 0x%08x\n"
+                    "microcode: Firmware update recommended\n", mc->rev);
+        return false;
+    }
+
+    return true;
+}
+
 static int cf_check intel_compare(
     const struct microcode_patch *old, const struct microcode_patch *new)
 {
@@ -365,6 +395,7 @@ static struct microcode_patch *cf_check intel_ucode_parse(
          * one with higher revision.
          */
         if ( microcode_fits_cpu(mc) &&
+             microcode_safe_to_load(mc) &&
              (!saved || compare_revisions(saved->rev, mc->rev) == NEW_UCODE) )
             saved = mc;
 
-- 
2.39.5