[PATCH v2] x86/ucode/AMD: apply the patch early on every logical thread

[Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>]

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. Late loading is still performed only on the first of SMT/CMT
siblings and only if a newer ucode revision has been provided (unless
allow_same option is specified).

Intel's side of things is modified for consistency but provides no
functional change.

Signed-off-by: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>
---
v1 --> v2:
- Expanded the commit message with the levelling section
- Adjusted comment for OLD_UCODE

CC: Jan Beulich <jbeulich@xxxxxxxx>
CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: "Roger Pau Monné" <roger.pau@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
---
 xen/arch/x86/cpu/microcode/amd.c     | 16 +++++++++++++---
 xen/arch/x86/cpu/microcode/intel.c   |  9 +++++++--
 xen/arch/x86/cpu/microcode/private.h |  3 ++-
 3 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/xen/arch/x86/cpu/microcode/amd.c b/xen/arch/x86/cpu/microcode/amd.c
index 4b097187a0..96db10a2e0 100644
--- a/xen/arch/x86/cpu/microcode/amd.c
+++ b/xen/arch/x86/cpu/microcode/amd.c
@@ -176,8 +176,13 @@ 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 )
+    {
+        if ( opt_ucode_allow_same )
+            return NEW_UCODE;
+        else
+            return SAME_UCODE;
+    }
 
     return OLD_UCODE;
 }
@@ -220,8 +225,13 @@ 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/intel.c 
b/xen/arch/x86/cpu/microcode/intel.c
index f7fec4b4ed..59a99eee4e 100644
--- a/xen/arch/x86/cpu/microcode/intel.c
+++ b/xen/arch/x86/cpu/microcode/intel.c
@@ -232,8 +232,13 @@ 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 )
+    {
+        if ( opt_ucode_allow_same )
+            return NEW_UCODE;
+        else
+            return SAME_UCODE;
+    }
 
     /*
      * Treat pre-production as always applicable - anyone using pre-production
diff --git a/xen/arch/x86/cpu/microcode/private.h 
b/xen/arch/x86/cpu/microcode/private.h
index 73b095d5bf..626aeb4d08 100644
--- 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 */
 };
-- 
2.17.1