[Xen-devel] [PATCH] Fix cache flush bug of cpu offline

["Liu, Jinsong" <jinsong.liu@xxxxxxxxx>]

Fix cache flush bug of cpu offline

Current xen cpu offline logic flush cache too early, which potentially break 
cache coherency.
wbinvd should be the last ops before cpu going into dead, otherwise cache may 
be dirty, 
i.e, something like setting an A bit on page tables. Pointed out by Arjan van 
de Ven.

Signed-off-by: Liu, Jinsong <jinsong.liu@xxxxxxxxx>

diff -r 2dc3c1cc1bba xen/arch/x86/acpi/cpu_idle.c
--- a/xen/arch/x86/acpi/cpu_idle.c      Mon Mar 07 05:31:46 2022 +0800
+++ b/xen/arch/x86/acpi/cpu_idle.c      Thu Mar 10 23:40:51 2022 +0800
@@ -562,11 +562,14 @@ static void acpi_dead_idle(void)
     if ( (cx = &power->states[power->count-1]) == NULL )
         goto default_halt;
 
+    /*
+     * cache must be flashed as the last ops before cpu going into dead,
+     * otherwise, cpu may dead with dirty data breaking cache coherency,
+     * leading to strange errors.
+     */
+    wbinvd();
     for ( ; ; )
     {
-        if ( !power->flags.bm_check && cx->type == ACPI_STATE_C3 )
-            ACPI_FLUSH_CPU_CACHE();
-
         switch ( cx->entry_method )
         {
             case ACPI_CSTATE_EM_FFH:
@@ -584,6 +587,7 @@ static void acpi_dead_idle(void)
     }
 
 default_halt:
+    wbinvd();
     for ( ; ; )
         halt();
 }
diff -r 2dc3c1cc1bba xen/arch/x86/domain.c
--- a/xen/arch/x86/domain.c     Mon Mar 07 05:31:46 2022 +0800
+++ b/xen/arch/x86/domain.c     Thu Mar 10 23:40:51 2022 +0800
@@ -93,6 +93,12 @@ static void default_idle(void)
 
 static void default_dead_idle(void)
 {
+    /*
+     * cache must be flashed as the last ops before cpu going into dead,
+     * otherwise, cpu may dead with dirty data breaking cache coherency,
+     * leading to strange errors.
+     */
+    wbinvd();
     for ( ; ; )
         halt();
 }
@@ -100,7 +106,6 @@ static void play_dead(void)
 static void play_dead(void)
 {
     local_irq_disable();
-    wbinvd();
 
     /*
      * NOTE: After cpu_exit_clear, per-cpu variables are no longer accessible,

Attachment: cpu_offline_1.patch
Description: cpu_offline_1.patch

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