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Re: [Xen-devel] RE: kernel panic when enable x2apic

To: Jan Beulich <JBeulich@xxxxxxxxxx>
Subject: Re: [Xen-devel] RE: kernel panic when enable x2apic
From: Weidong Han <weidong.han@xxxxxxxxx>
Date: Tue, 30 Nov 2010 16:50:11 +0800
Cc: "Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx>, Sander Eikelenboom <linux@xxxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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Jan Beulich wrote:
On 19.11.10 at 11:40, Sander Eikelenboom <linux@xxxxxxxxxxxxxx> wrote:
Hello Jan,

Friday, November 19, 2010, 11:17:21 AM, you wrote:

On 18.11.10 at 05:53, "Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx> wrote:
From this output, it shows the cpupool_id = 7f034000, I don't know why it was 7f034000. I think the first cpupool_id should be 0?Am I right?
Yes, it ought to be zero.
Also the fail with write mtrr MSR, the value also is very strange: ffff83007f0f7670, it totally different with the SDM says.
(XEN) MTRR: CPU 0: Writing MSR 200 to ffff83007f0f7670 failed
Yes, I had indicated so in an earlier reply.
So, I am think that maybe the heap is broken?
General memory corruption is more likely. The question is when it
General memory corruption could also be hardware related (bad dimm) ?

In general, yes, but this wouldn't normally lead to patterns that look
like valid (albeit misplaced) addresses, I would think.


We root caused this issue. Actually it is not related to x2APIC and c/s 22375, it's caused by incorrectly setting boot_cpu_data.x86_capability. boot_cpu_data.x86_capability is set in identify_cpu, but I found boot_cpu_data.x86_capability[4] is also set in start_vmx, which may overwrite the previous values. This panic is caused by overwriting X86_FEATURE_XSAVE bit in boot_cpu_data.x86_capability. Yang's platform support xsave, and xsave is not enabled (by default), then X86_FEATURE_XSAVE bit will be cleared in boot_cpu_data.x86_capability in init_intel, that means cpu_has_xsave is 0. But later, start_vmx set that bit (cpu_has_xsave is true) again. This results in Xen to allocate xsave area in vcpu_initialise, we observed it may allocate a used address for it, therefore cause the panic. The obvious solution is to remove boot_cpu_data.x86_capability[4] = cpuid_ecx(1) in start_vmx. It indeed works with the change. I will send out the patch after more tests.


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