>From 4bfa45935c791c28814565cd261f4d5ff640653c Mon Sep 17 00:00:00 2001
From: Juergen Gross <jgross@xxxxxxxx>
To: xen-devel@xxxxxxxxxxxxxxxxxxxx
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: Wei Liu <wl@xxxxxxx>
Cc: "Roger Pau Monné" <roger.pau@xxxxxxxxxx>
Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: Julien Grall <julien@xxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Date: Thu, 6 Feb 2020 15:39:32 +0100
Subject: [PATCH] xen: make sure stop_machine_run() is always called in a
 tasklet

With core scheduling active it is mandatory for stop_machine_run() to
be called in a tasklet only.

Put a BUG_ON() into stop_machine_run() to test for this being sure
and adapt the missing call site (ucode loading).

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 xen/arch/x86/microcode.c  | 54 +++++++++++++++++++++++++++++------------------
 xen/common/stop_machine.c |  1 +
 2 files changed, 35 insertions(+), 20 deletions(-)

diff --git a/xen/arch/x86/microcode.c b/xen/arch/x86/microcode.c
index c0fb690f79..3efdf8269a 100644
--- a/xen/arch/x86/microcode.c
+++ b/xen/arch/x86/microcode.c
@@ -561,30 +561,18 @@ static int do_microcode_update(void *patch)
     return ret;
 }
 
-int microcode_update(XEN_GUEST_HANDLE_PARAM(const_void) buf, unsigned long len)
+struct ucode_buf {
+    unsigned long len;
+    char buffer[];
+};
+
+static long microcode_update_helper(void *data)
 {
     int ret;
-    void *buffer;
+    struct ucode_buf *buffer = data;
     unsigned int cpu, updated;
     struct microcode_patch *patch;
 
-    if ( len != (uint32_t)len )
-        return -E2BIG;
-
-    if ( microcode_ops == NULL )
-        return -EINVAL;
-
-    buffer = xmalloc_bytes(len);
-    if ( !buffer )
-        return -ENOMEM;
-
-    ret = copy_from_guest(buffer, buf, len);
-    if ( ret )
-    {
-        xfree(buffer);
-        return -EFAULT;
-    }
-
     /* cpu_online_map must not change during update */
     if ( !get_cpu_maps() )
     {
@@ -606,7 +594,7 @@ int microcode_update(XEN_GUEST_HANDLE_PARAM(const_void) buf, unsigned long len)
         return -EPERM;
     }
 
-    patch = parse_blob(buffer, len);
+    patch = parse_blob(buffer->buffer, buffer->len);
     xfree(buffer);
     if ( IS_ERR(patch) )
     {
@@ -699,6 +687,32 @@ int microcode_update(XEN_GUEST_HANDLE_PARAM(const_void) buf, unsigned long len)
     return ret;
 }
 
+int microcode_update(XEN_GUEST_HANDLE_PARAM(const_void) buf, unsigned long len)
+{
+    int ret;
+    struct ucode_buf *buffer;
+
+    if ( len != (uint32_t)len )
+        return -E2BIG;
+
+    if ( microcode_ops == NULL )
+        return -EINVAL;
+
+    buffer = xmalloc_bytes(len + sizeof(*buffer));
+    if ( !buffer )
+        return -ENOMEM;
+
+    ret = copy_from_guest(buffer->buffer, buf, len);
+    if ( ret )
+    {
+        xfree(buffer);
+        return -EFAULT;
+    }
+    buffer->len = len;
+
+    return continue_hypercall_on_cpu(0, microcode_update_helper, buffer);
+}
+
 static int __init microcode_init(void)
 {
     /*
diff --git a/xen/common/stop_machine.c b/xen/common/stop_machine.c
index 33d9602217..fe7f7d4447 100644
--- a/xen/common/stop_machine.c
+++ b/xen/common/stop_machine.c
@@ -74,6 +74,7 @@ int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
     int ret;
 
     BUG_ON(!local_irq_is_enabled());
+    BUG_ON(!is_idle_vcpu(current));
 
     /* cpu_online_map must not change. */
     if ( !get_cpu_maps() )
-- 
2.16.4