[Xen-devel] [PATCH v9 15/15] microcode: block #NMI handling when loading an ucode

[Chao Gao <chao.gao@intel.com>]

register an nmi callback. And this callback does busy-loop on threads
which are waiting for loading completion. Control threads send NMI to
slave threads to prevent NMI acceptance during ucode loading.

Signed-off-by: Chao Gao <chao.gao@intel.com>
---
Changes in v9:
 - control threads send NMI to all other threads. Slave threads will
 stay in the NMI handling to prevent NMI acceptance during ucode
 loading. Note that self-nmi is invalid according to SDM.
 - s/rep_nop/cpu_relax
 - remove debug message in microcode_nmi_callback(). Printing debug
 message would take long times and control thread may timeout.
 - rebase and fix conflicts

Changes in v8:
 - new
---
 xen/arch/x86/microcode.c | 28 ++++++++++++++++++++++------
 1 file changed, 22 insertions(+), 6 deletions(-)

diff --git a/xen/arch/x86/microcode.c b/xen/arch/x86/microcode.c
index 91f9e81..d943835 100644
--- a/xen/arch/x86/microcode.c
+++ b/xen/arch/x86/microcode.c
@@ -38,6 +38,7 @@
 
 #include <asm/delay.h>
 #include <asm/msr.h>
+#include <asm/nmi.h>
 #include <asm/processor.h>
 #include <asm/setup.h>
 #include <asm/microcode.h>
@@ -339,14 +340,8 @@ static int microcode_update_cpu(const struct microcode_patch *patch)
 
 static int slave_thread_fn(void)
 {
-    unsigned int cpu = smp_processor_id();
     unsigned int master = cpumask_first(this_cpu(cpu_sibling_mask));
 
-    while ( loading_state != LOADING_CALLIN )
-        cpu_relax();
-
-    cpumask_set_cpu(cpu, &cpu_callin_map);
-
     while ( loading_state != LOADING_EXIT )
         cpu_relax();
 
@@ -399,6 +394,8 @@ static int control_thread_fn(const struct microcode_patch *patch)
 
     cpumask_set_cpu(cpu, &cpu_callin_map);
 
+    smp_send_nmi_allbutself();
+
     /* Waiting for all threads calling in */
     ret = wait_for_condition(wait_cpu_callin,
                              (void *)(unsigned long)num_online_cpus(),
@@ -481,12 +478,28 @@ static int do_microcode_update(void *patch)
     return ret;
 }
 
+static int microcode_nmi_callback(const struct cpu_user_regs *regs, int cpu)
+{
+    /* The first thread of a core is to load an update. Don't block it. */
+    if ( cpu == cpumask_first(per_cpu(cpu_sibling_mask, cpu)) ||
+         loading_state != LOADING_CALLIN )
+        return 0;
+
+    cpumask_set_cpu(cpu, &cpu_callin_map);
+
+    while ( loading_state != LOADING_EXIT )
+        cpu_relax();
+
+    return 0;
+}
+
 int microcode_update(XEN_GUEST_HANDLE_PARAM(const_void) buf, unsigned long len)
 {
     int ret;
     void *buffer;
     unsigned int cpu, updated;
     struct microcode_patch *patch;
+    nmi_callback_t *saved_nmi_callback;
 
     if ( len != (uint32_t)len )
         return -E2BIG;
@@ -551,6 +564,8 @@ int microcode_update(XEN_GUEST_HANDLE_PARAM(const_void) buf, unsigned long len)
      * watchdog timeout.
      */
     watchdog_disable();
+
+    saved_nmi_callback = set_nmi_callback(microcode_nmi_callback);
     /*
      * Late loading dance. Why the heavy-handed stop_machine effort?
      *
@@ -563,6 +578,7 @@ int microcode_update(XEN_GUEST_HANDLE_PARAM(const_void) buf, unsigned long len)
      *   conservative and good.
      */
     ret = stop_machine_run(do_microcode_update, patch, NR_CPUS);
+    set_nmi_callback(saved_nmi_callback);
     watchdog_enable();
 
     updated = atomic_read(&cpu_updated);
-- 
1.8.3.1


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