[Xen-devel] [PATCH v3 for 4.13] x86/microcode: refuse to load the same revision ucode

[Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>]

Currently if a user tries to live-load the same or older ucode revision
than CPU already has, he will get a single message in Xen log like:

    (XEN) 128 cores are to update their microcode

No actual ucode loading will happen and this situation can be quite
confusing. Fix this by starting ucode update only when the provided
ucode revision is higher than the currently cached one (if any).
This is based on the property that if microcode_cache exists, all CPUs
in the system should have at least that ucode revision.

Additionally, print a user friendly message if no matching or newer
ucode can be found in the provided blob. This also requires ignoring
-ENODATA in AMD-side code, otherwise the message given to the user is:

    (XEN) Parsing microcode blob error -61

Which actually means that a ucode blob was parsed fine, but no matching
ucode was found.

Signed-off-by: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>
---
v2 --> v3:
- move ucode comparison to generic code
- ignore -ENODATA in a different code section

v1 --> v2:
- compare provided ucode with the currently cached one

CC: Jan Beulich <jbeulich@xxxxxxxx>
CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Chao Gao <chao.gao@xxxxxxxxx>
CC: Juergen Gross <jgross@xxxxxxxx>
---
 xen/arch/x86/microcode.c     | 19 +++++++++++++++++++
 xen/arch/x86/microcode_amd.c |  7 +++++++
 2 files changed, 26 insertions(+)

diff --git a/xen/arch/x86/microcode.c b/xen/arch/x86/microcode.c
index 65d1f41e7c..44efc2d9b3 100644
--- a/xen/arch/x86/microcode.c
+++ b/xen/arch/x86/microcode.c
@@ -640,10 +640,29 @@ int microcode_update(XEN_GUEST_HANDLE_PARAM(const_void) 
buf, unsigned long len)
 
     if ( !patch )
     {
+        printk(XENLOG_WARNING "microcode: couldn't find any matching ucode in "
+                              "the provided blob!\n");
         ret = -ENOENT;
         goto put;
     }
 
+    /*
+     * If microcode_cache exists, all CPUs in the system should have at least
+     * that ucode revision.
+     */
+    spin_lock(&microcode_mutex);
+    if ( microcode_cache &&
+         microcode_ops->compare_patch(patch, microcode_cache) != NEW_UCODE )
+    {
+        spin_unlock(&microcode_mutex);
+        printk(XENLOG_WARNING "microcode: couldn't find any newer revision "
+                              "in the provided blob!\n");
+        ret = -ENOENT;
+
+        goto put;
+    }
+    spin_unlock(&microcode_mutex);
+
     if ( microcode_ops->start_update )
     {
         ret = microcode_ops->start_update();
diff --git a/xen/arch/x86/microcode_amd.c b/xen/arch/x86/microcode_amd.c
index 1e52f7f49a..00750f7bbb 100644
--- a/xen/arch/x86/microcode_amd.c
+++ b/xen/arch/x86/microcode_amd.c
@@ -502,6 +502,13 @@ static struct microcode_patch *cpu_request_microcode(const 
void *buf,
 
     if ( error )
     {
+        /*
+         * -ENODATA here means that the blob was parsed fine but no matching
+         * ucode was found. Don't return it to the caller.
+         */
+        if ( error == -ENODATA )
+            error = 0;
+
         xfree(mc_amd->equiv_cpu_table);
         xfree(mc_amd);
         goto out;
-- 
2.17.1


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