[Xen-devel] [PATCH] Fix cpu offline bug: cancel SYSIO method when play dead

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

Fix cpu offline bug: cancel SYSIO method when play dead

Play dead is a fragile and tricky point of cpu offline logic.
For how to play cpu dead, linux kernel changed several times:
Very old kernel support 3 ways to play cpu dead: mwait, SYSIO, and halt, just 
like what cpuidle did when enter C3;
Later, it cancel mwait and SYSIO support, only use halt to play dead;
Latest linux 2.6.38 add mwait support when cpu dead.

This patch cancel SYSIO method when cpu dead, keep same with latest kernel. 

SYSIO is an obsoleted method to enter deep C, with some tricky hardware 
behavior, and seldom supported in new platform.
Xen experiment indicate that when cpu dead, SYSIO method would trigger unknown 
issue which would bring strange error.
We now cancel SYSIO method when cpu dead, after all, correctness is more 
important than power save, and btw new platform use mwait.

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

diff -r c622e93f69a0 xen/arch/x86/acpi/cpu_idle.c
--- a/xen/arch/x86/acpi/cpu_idle.c      Thu Mar 10 23:40:52 2022 +0800
+++ b/xen/arch/x86/acpi/cpu_idle.c      Fri Mar 11 03:45:31 2022 +0800
@@ -554,7 +554,6 @@ static void acpi_dead_idle(void)
 {
     struct acpi_processor_power *power;
     struct acpi_processor_cx *cx;
-    int unused;
 
     if ( (power = processor_powers[smp_processor_id()]) == NULL )
         goto default_halt;
@@ -576,10 +575,6 @@ static void acpi_dead_idle(void)
                 /* Not treat interrupt as break event */
                 __monitor((void *)&mwait_wakeup(smp_processor_id()), 0, 0);
                 __mwait(cx->address, 0);
-                break;
-            case ACPI_CSTATE_EM_SYSIO:
-                inb(cx->address);
-                unused = inl(pmtmr_ioport);
                 break;
             default:
                 goto default_halt;

Attachment: cpu_offline_2.patch
Description: cpu_offline_2.patch

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