RE: [Xen-devel] [PATCH] When flush tlb , we need consider the cpu_online_map

["Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>]

Sure.Attached is the new patch. 

BTW, Xiantao will have a look on the two cpu_clear(cpu, cpu_online_map) in 
__cpu_disable(), so I remove the comments in the patch.

Thanks
--jyh


When flush tlb mask, we need consider the cpu_online_map. The same happens to 
ept flush also.

We noticed sometime system hang on cpu online/offline stress test. The reason 
is because flush_tlb_mask from __get_page_type is deadloop.

This should be caused by a small windows in cpu offline.
The cpu_online_map is changed and the interrupt is disabled at take_cpu_down() 
for the to-be-offline CPU.

However, the __sync_lazy_execstate() called from idle_task_exit() in the 
idle_loop() for the to-be-offline CPU. At that time, the stop_machine_run is 
finished already, and __get_page_type may be called in other CPU before the 
__sync_lazy_execstate().

Thanks Jan pointing out issue in my original patch and gives suggestion, not 
sure if he would like be in the signed-off-by.

Signed-off-by: Jiang, Yunhong <yunhong.jiang@xxxxxxxxx>

diff -r f3db0ae08304 xen/arch/x86/hvm/vmx/vmx.c
--- a/xen/arch/x86/hvm/vmx/vmx.c        Sat Mar 27 16:01:35 2010 +0000
+++ b/xen/arch/x86/hvm/vmx/vmx.c        Tue Mar 30 11:07:33 2010 +0800
@@ -1234,7 +1234,9 @@ void ept_sync_domain(struct domain *d)
      * the ept_synced mask before on_selected_cpus() reads it, resulting in
      * unnecessary extra flushes, to avoid allocating a cpumask_t on the stack.
      */
-    d->arch.hvm_domain.vmx.ept_synced = d->domain_dirty_cpumask;
+    cpus_and(d->arch.hvm_domain.vmx.ept_synced,
+                 d->domain_dirty_cpumask, cpu_online_map);
+
     on_selected_cpus(&d->arch.hvm_domain.vmx.ept_synced,
                      __ept_sync_domain, d, 1);
 }
diff -r f3db0ae08304 xen/arch/x86/smp.c
--- a/xen/arch/x86/smp.c        Sat Mar 27 16:01:35 2010 +0000
+++ b/xen/arch/x86/smp.c        Tue Mar 30 11:06:59 2010 +0800
@@ -228,7 +228,8 @@ void flush_area_mask(const cpumask_t *ma
     if ( !cpus_subset(*mask, *cpumask_of(smp_processor_id())) )
     {
         spin_lock(&flush_lock);
-        cpus_andnot(flush_cpumask, *mask, *cpumask_of(smp_processor_id()));
+        cpus_and(flush_cpumask, *mask, cpu_online_map);
+        cpu_clear(smp_processor_id(), flush_cpumask);
         flush_va      = va;
         flush_flags   = flags;
         send_IPI_mask(&flush_cpumask, INVALIDATE_TLB_VECTOR);



>-----Original Message-----
>From: Keir Fraser [mailto:keir.fraser@xxxxxxxxxxxxx]
>Sent: Monday, March 29, 2010 10:33 PM
>To: Jan Beulich; Jiang, Yunhong
>Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
>Subject: Re: [Xen-devel] [PATCH] When flush tlb , we need consider the
>cpu_online_map
>
>Sounds good. Can you please re-spin the patch, Yunhong? I will drop your
>original patch for now.
>
> -- Keir
>
>On 29/03/2010 13:55, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:
>
>>>>> "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx> 29.03.10 14:00 >>>
>>> When flush tlb mask, we need consider the cpu_online_map. The same happens
>to
>>> ept flush also.
>>
>> While the idea is certainly correct, doing this more efficiently seems
>> quite desirable to me, especially when NR_CPUS is large:
>>
>>> --- a/xen/arch/x86/hvm/vmx/vmx.c Sat Mar 27 16:01:35 2010 +0000
>>> +++ b/xen/arch/x86/hvm/vmx/vmx.c Mon Mar 29 17:49:51 2010 +0800
>>> @@ -1235,6 +1235,9 @@ void ept_sync_domain(struct domain *d)
>>>      * unnecessary extra flushes, to avoid allocating a cpumask_t on the
>>> stack.
>>>      */
>>>     d->arch.hvm_domain.vmx.ept_synced = d->domain_dirty_cpumask;
>>> +    cpus_and(d->arch.hvm_domain.vmx.ept_synced,
>>> +             d->arch.hvm_domain.vmx.ept_synced,
>>> +             cpu_online_map);
>>
>> The added code can be combined with the pre-existing line:
>>
>>     cpus_and(d->arch.hvm_domain.vmx.ept_synced,
>>              d->domain_dirty_cpumask, cpu_online_map);
>>
>>>     on_selected_cpus(&d->arch.hvm_domain.vmx.ept_synced,
>>>                      __ept_sync_domain, d, 1);
>>> }
>>> --- a/xen/arch/x86/smp.c Sat Mar 27 16:01:35 2010 +0000
>>> +++ b/xen/arch/x86/smp.c Mon Mar 29 17:47:25 2010 +0800
>>> @@ -229,6 +229,7 @@ void flush_area_mask(const cpumask_t *ma
>>>     {
>>>         spin_lock(&flush_lock);
>>>         cpus_andnot(flush_cpumask, *mask,
>*cpumask_of(smp_processor_id()));
>>> +        cpus_and(flush_cpumask, cpu_online_map, flush_cpumask);
>>
>> Here, first doing the full-mask operation and then clearing the one
>> extra bit is less overhead:
>>
>>         cpus_and(flush_cpumask, *mask, cpu_online_map);
>>         cpu_clear(smp_processor_id(), flush_cpumask);
>>
>>>         flush_va      = va;
>>>         flush_flags   = flags;
>>>         send_IPI_mask(&flush_cpumask, INVALIDATE_TLB_VECTOR);
>>
>> Jan
>>
>>
>>
>

Attachment: flush_tlb_map.patch
Description: flush_tlb_map.patch

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