x86/ucode: allow cpu_request_microcode() to skip memory allocation

This is a preparatory step in order to do earlier microcode loading on
the boot CPU when the domain heap has not been initialized yet and
xmalloc still unavailable.

Add make_copy argument which will allow to load microcode directly from
the blob bypassing microcode_cache.

Signed-off-by: Sergey Dyasli <sergey.dyasli@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/cpu/microcode/amd.c

@@ -300,7 +300,7 @@ static int scan_equiv_cpu_table(const struct container_equiv_table *et)
 }
 
 static struct microcode_patch *cf_check cpu_request_microcode(
-    const void *buf, size_t size)
+    const void *buf, size_t size, bool make_copy)
 {
     const struct microcode_patch *saved = NULL;
     struct microcode_patch *patch = NULL;
@@ -411,9 +411,14 @@ static struct microcode_patch *cf_check cpu_request_microcode(
 
     if ( saved )
     {
-        patch = xmemdup_bytes(saved, saved_size);
-        if ( !patch )
-            error = -ENOMEM;
+        if ( make_copy )
+        {
+            patch = xmemdup_bytes(saved, saved_size);
+            if ( !patch )
+                error = -ENOMEM;
+        }
+        else
+            patch = (struct microcode_patch *)saved;
     }
 
     if ( error && !patch )

xen/arch/x86/cpu/microcode/core.c

@@ -244,7 +244,7 @@ static struct microcode_patch *parse_blob(const char *buf, size_t len)
 {
     alternative_vcall(ucode_ops.collect_cpu_info);
 
-    return alternative_call(ucode_ops.cpu_request_microcode, buf, len);
+    return alternative_call(ucode_ops.cpu_request_microcode, buf, len, true);
 }
 
 static void microcode_free_patch(struct microcode_patch *patch)

xen/arch/x86/cpu/microcode/intel.c

@@ -324,7 +324,7 @@ static int cf_check apply_microcode(const struct microcode_patch *patch)
 }
 
 static struct microcode_patch *cf_check cpu_request_microcode(
-    const void *buf, size_t size)
+    const void *buf, size_t size, bool make_copy)
 {
     int error = 0;
     const struct microcode_patch *saved = NULL;
@@ -364,10 +364,15 @@ static struct microcode_patch *cf_check cpu_request_microcode(
 
     if ( saved )
     {
-        patch = xmemdup_bytes(saved, get_totalsize(saved));
+        if ( make_copy )
+        {
+            patch = xmemdup_bytes(saved, get_totalsize(saved));
 
-        if ( !patch )
-            error = -ENOMEM;
+            if ( !patch )
+                error = -ENOMEM;
+        }
+        else
+            patch = (struct microcode_patch *)saved;
     }
 
     if ( error && !patch )

xen/arch/x86/cpu/microcode/private.h

@@ -23,15 +23,21 @@ struct microcode_ops {
      * older that what is running in the CPU.  This is a feature, to better
      * cope with corner cases from buggy firmware.)
      *
-     * If one is found, allocate and return a struct microcode_patch
-     * encapsulating the appropriate microcode patch.  Does not alias the
-     * original buffer.  Must be suitable to be freed with a single xfree().
+     * If one is found, behaviour depends on the make_copy argument:
+     *
+     *     true: allocate and return a struct microcode_patch encapsulating
+     *           the appropriate microcode patch.  Does not alias the original
+     *           buffer.  Must be suitable to be freed with a single xfree().
+     *
+     *    false: return a pointer to the patch within the original buffer.
+     *           This is useful for early microcode loading when xmalloc might
+     *           not be available yet.
      *
      * If one is not found, (nothing matches the current CPU), return NULL.
      * Also may return ERR_PTR(-err), e.g. bad container, out of memory.
      */
-    struct microcode_patch *(*cpu_request_microcode)(const void *buf,
-                                                     size_t size);
+    struct microcode_patch *(*cpu_request_microcode)(
+        const void *buf, size_t size, bool make_copy);
 
     /*
      * Obtain microcode-relevant details for the current CPU.  Results in