x86/ucode/AMD: apply the patch early on every logical thread

The original issue has been reported on AMD Bulldozer-based CPUs where
ucode loading loses the LWP feature bit in order to gain the IBPB bit.
LWP disabling is per-SMT/CMT core modification and needs to happen on
each sibling thread despite the shared microcode engine. Otherwise,
logical CPUs will end up with different cpuid capabilities.
Link: https://bugzilla.kernel.org/show_bug.cgi?id=216211
Guests running under Xen happen to be not affected because of levelling
logic for the feature masking/override MSRs which causes the LWP bit to
fall out and hides the issue. The latest recommendation from AMD, after
discussing this bug, is to load ucode on every logical CPU.

In Linux kernel this issue has been addressed by e7ad18d1169c
("x86/microcode/AMD: Apply the patch early on every logical thread").
Follow the same approach in Xen.

Introduce SAME_UCODE match result and use it for early AMD ucode
loading. Take this opportunity and move opt_ucode_allow_same out of
compare_revisions() to the relevant callers and also modify the warning
message based on it. Intel's side of things is modified for consistency
but provides no functional change.

Signed-off-by: Sergey Dyasli <sergey.dyasli@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: f4ef8a41b80831db2136bdaff9f946a1a4b051e7
master date: 2023-02-21 15:08:05 +0100

diff --git a/xen/arch/x86/cpu/microcode/amd.c b/xen/arch/x86/cpu/microcode/amd.c
index 8195707ee1496e024e43d6dabe30d41b0feb0381..ded8fe90e6505b3d28f542f556224456ff3ffef3 100644 (file)
--- a/xen/arch/x86/cpu/microcode/amd.c
+++ b/xen/arch/x86/cpu/microcode/amd.c
@@ -176,8 +176,8 @@ static enum microcode_match_result compare_revisions(
     if ( new_rev > old_rev )
         return NEW_UCODE;
 
-    if ( opt_ucode_allow_same && new_rev == old_rev )
-        return NEW_UCODE;
+    if ( new_rev == old_rev )
+        return SAME_UCODE;
 
     return OLD_UCODE;
 }
@@ -220,8 +220,13 @@ static int cf_check apply_microcode(const struct microcode_patch *patch)
     unsigned int cpu = smp_processor_id();
     struct cpu_signature *sig = &per_cpu(cpu_sig, cpu);
     uint32_t rev, old_rev = sig->rev;
+    enum microcode_match_result result = microcode_fits(patch);
 
-    if ( microcode_fits(patch) != NEW_UCODE )
+    /*
+     * Allow application of the same revision to pick up SMT-specific changes
+     * even if the revision of the other SMT thread is already up-to-date.
+     */
+    if ( result != NEW_UCODE && result != SAME_UCODE )
         return -EINVAL;
 
     if ( check_final_patch_levels(sig) )

diff --git a/xen/arch/x86/cpu/microcode/core.c b/xen/arch/x86/cpu/microcode/core.c
index 452a7ca7734035ff4b399665e1a9cb2c4de81866..57ecc5358bdfa5b627aa760df8d1bddb171ea8da 100644 (file)
--- a/xen/arch/x86/cpu/microcode/core.c
+++ b/xen/arch/x86/cpu/microcode/core.c
@@ -610,17 +610,25 @@ static long cf_check microcode_update_helper(void *data)
      * that ucode revision.
      */
     spin_lock(&microcode_mutex);
-    if ( microcode_cache &&
-         alternative_call(ucode_ops.compare_patch,
-                          patch, microcode_cache) != NEW_UCODE )
+    if ( microcode_cache )
     {
-        spin_unlock(&microcode_mutex);
-        printk(XENLOG_WARNING "microcode: couldn't find any newer revision "
-                              "in the provided blob!\n");
-        microcode_free_patch(patch);
-        ret = -ENOENT;
+        enum microcode_match_result result;
 
-        goto put;
+        result = alternative_call(ucode_ops.compare_patch, patch,
+                                  microcode_cache);
+
+        if ( result != NEW_UCODE &&
+             !(opt_ucode_allow_same && result == SAME_UCODE) )
+        {
+            spin_unlock(&microcode_mutex);
+            printk(XENLOG_WARNING
+                   "microcode: couldn't find any newer%s revision in the provided blob!\n",
+                   opt_ucode_allow_same ? " (or the same)" : "");
+            microcode_free_patch(patch);
+            ret = -ENOENT;
+
+            goto put;
+        }
     }
     spin_unlock(&microcode_mutex);
 

diff --git a/xen/arch/x86/cpu/microcode/intel.c b/xen/arch/x86/cpu/microcode/intel.c
index f5ba6d76d7240298f391468ca682a07c60860f50..cb08f63d2e4a1286965abf001e93f7b83cfdcd11 100644 (file)
--- a/xen/arch/x86/cpu/microcode/intel.c
+++ b/xen/arch/x86/cpu/microcode/intel.c
@@ -232,8 +232,8 @@ static enum microcode_match_result compare_revisions(
     if ( new_rev > old_rev )
         return NEW_UCODE;
 
-    if ( opt_ucode_allow_same && new_rev == old_rev )
-        return NEW_UCODE;
+    if ( new_rev == old_rev )
+        return SAME_UCODE;
 
     /*
      * Treat pre-production as always applicable - anyone using pre-production
@@ -290,8 +290,12 @@ static int cf_check apply_microcode(const struct microcode_patch *patch)
     unsigned int cpu = smp_processor_id();
     struct cpu_signature *sig = &this_cpu(cpu_sig);
     uint32_t rev, old_rev = sig->rev;
+    enum microcode_match_result result;
+
+    result = microcode_update_match(patch);
 
-    if ( microcode_update_match(patch) != NEW_UCODE )
+    if ( result != NEW_UCODE &&
+         !(opt_ucode_allow_same && result == SAME_UCODE) )
         return -EINVAL;
 
     wbinvd();

diff --git a/xen/arch/x86/cpu/microcode/private.h b/xen/arch/x86/cpu/microcode/private.h
index c085a10268471869ba2369de935433cfbdc996fc..feafab0677a16e3189545a30388f5511b0b13a6f 100644 (file)
--- a/xen/arch/x86/cpu/microcode/private.h
+++ b/xen/arch/x86/cpu/microcode/private.h
@@ -6,7 +6,8 @@
 extern bool opt_ucode_allow_same;
 
 enum microcode_match_result {
-    OLD_UCODE, /* signature matched, but revision id is older or equal */
+    OLD_UCODE, /* signature matched, but revision id is older */
+    SAME_UCODE, /* signature matched, but revision id is the same */
     NEW_UCODE, /* signature matched, but revision id is newer */
     MIS_UCODE, /* signature mismatched */
 };