RE: [Xen-devel] [PATCH] Fixing PAE SMP dom0 hang at boot time

["Nakajima, Jun" <jun.nakajima@xxxxxxxxx>]

Ryan Harper wrote:
> * Nakajima, Jun <jun.nakajima@xxxxxxxxx> [2005-11-16 11:42]:
>> Ryan Harper wrote:
>>> * Nakajima, Jun <jun.nakajima@xxxxxxxxx> [2005-11-15 19:56]:
>>>> This patch fixes a hang with PAE SMP dom0 on big SMP machines. As
>>>> far as I tested, 8-way PAE SMP dom0 boots fine on >=8-way machines.
>>>> The fix is not PAE specific, and I made the equivent changes to
>>>> x86_64 xenlinux. Tested on both PAE and x86_64 dom0 xenlinux on
>>>>> =8-way SMP machines with
>>>>> 6GB.
>>> 
>>> Jun,  could you explain the patch a bit more?
>>> 
>>> Why wouldn't we want to initialize the per-cpu gdt area for cpus
>>> other than CPU0 ? 
>>> 
>>> -       cpu_gdt_init(&cpu_gdt_descr[cpu]);
>>> +       if (!cpu)
>>> +           cpu_gdt_init(&cpu_gdt_descr[cpu]);
>> 
>> CPU0 creates the (virutal) gdt for other CPUs in advance at
>> VCPUOP_initalise, and the propoer selector values are set up at the
>> same. So it's redundant. It also avoids spurious page faults caused
>> by make_page_readonly() against the gdt page.
> 
> OK.  Thanks for the explaination.  With this patch, we are still
> seeing the revised set_gdt() issue (comment 18 on bug 366) on our
> 32-way. We've don't seen the hang except when we have 8 cpus instead
> of the full 
> 32.

Yes, I'm aware of that, and updated the bugzilla. I believe it's not an
SMP problem, but probably is caused by 16GB memory or copy_from_user()
(for PAE with large memory). Anyway, let's use the bugzilla.

Jun
---
Intel Open Source Technology Center

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