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Re: [Xen-devel] [PATCH v2 6/6] xen/arm: update the docs about heterogeneous computing



Hi Stefano,

On 19/02/18 21:58, Stefano Stabellini wrote:
diff --git a/docs/misc/xen-command-line.markdown 
b/docs/misc/xen-command-line.markdown
index 2184cb9..8997904 100644
--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -1007,7 +1007,12 @@ Control Xens use of the APEI Hardware Error Source 
Table, should one be found.
Say yes at your own risk if you want to enable heterogenous computing
  (such as big.LITTLE). This may result to an unstable and insecure
-platform. When the option is disabled (default), CPUs that are not
+platform, unless you manually specify the cpu affinity of all domains so
+that all vcpus are scheduled on the same class of pcpus (big or LITTLE
+but not both). vcpu migration between big cores and LITTLE cores is not
+supported. See docs/misc/arm/big.LITTLE.txt for more information.
+
+When the hmp-unsafe option is disabled (default), CPUs that are not
  identical to the boot CPU will be parked and not used by Xen.
### hpetbroadcast
diff --git a/xen/arch/arm/smpboot.c b/xen/arch/arm/smpboot.c
index 122c0b5..d04b7c7 100644
--- a/xen/arch/arm/smpboot.c
+++ b/xen/arch/arm/smpboot.c
@@ -266,7 +266,7 @@ void __init smp_init_cpus(void)
if ( opt_hmp_unsafe )
          warning_add("WARNING: HMP COMPUTING HAS BEEN ENABLED.\n"
-                    "It has implications on the security and stability of the 
system.\n");
+                    "It has implications on the security and stability of the 
system, unless the cpu affinity of all domains is specified.\n");

The warning message will not be print nicely on serial. Please make sure it is split at 72 characters.

  }
int __init
@@ -308,13 +308,14 @@ void start_secondary(unsigned long boot_phys_offset,
      /*
       * Currently Xen assumes the platform has only one kind of CPUs.
       * This assumption does not hold on big.LITTLE platform and may
-     * result to instability and insecure platform. Better to park them
-     * for now.
+     * result to instability and insecure platform (unless cpu affinity
+     * is manually specified for all domains). Better to park them for
+     * now.
       */
      if ( !opt_hmp_unsafe &&
           current_cpu_data.midr.bits != boot_cpu_data.midr.bits )
      {
-        printk(XENLOG_ERR "CPU%u MIDR (0x%x) does not match boot CPU MIDR 
(0x%x).\n",
+        printk(XENLOG_ERR "CPU%u MIDR (0x%x) does not match boot CPU MIDR (0x%x), 
disable cpu (see big.LITTLE.txt under docs/).\n",

Same here.

                 smp_processor_id(), current_cpu_data.midr.bits,
                 boot_cpu_data.midr.bits);
          stop_cpu();


Cheers,

--
Julien Grall

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