linux-kernel - Re: [Xen-devel] PROBLEM: kernel panic xsave

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Date:	Tue, 20 Oct 2015 14:11:45 +0200
From:	John Doe <securef33d@...il.com>
To:	Jan Beulich <JBeulich@...e.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:	Ingo Molnar <mingo@...nel.org>, x86@...nel.org,
	xen-devel@...ts.xen.org, linux-kernel@...r.kernel.org
Subject: Re: [Xen-devel] PROBLEM: kernel panic xsave_init

On 20/10/2015 11:51, Jan Beulich wrote:
>>>> On 19.10.15 at 18:25, <boris.ostrovsky@...cle.com> wrote:
>> On 10/19/2015 06:16 AM, John Doe wrote:
>>>>> [    0.000000] general protection fault: 0000 [#1] SMP
>>>>> [    0.000000] Modules linked in:
>>>>> [    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 
>> 4.1.9-6.pvops.qubes.x86_64 #1
>>>>> [    0.000000] Hardware name: To Be Filled By O.E.M. To Be Filled By 
>> O.E.M./Z170 Extreme4, BIOS P1.80 09/18/2015
>>>>> [    0.000000] task: ffffffff81c154c0 ti: ffffffff81c00000 task.ti: 
>> ffffffff81c00000
>>>>> [    0.000000] RIP: e030:[<ffffffff81d58fad>]  [<ffffffff81d58fad>] 
>> xstate_enable_boot_cpu+0xde/0x288
>>>>> [    0.000000] RSP: e02b:ffffffff81c03de8  EFLAGS: 00010046
>>>>> [    0.000000] RAX: 000000000000001f RBX: 0000000000000008 RCX: 
>> 0000000000000000
>>>>> [    0.000000] RDX: 0000000000000000 RSI: 000000000000001f RDI: 
>> 0000000000042660
>>
>>
>> It would be good to see what's at ffffffff81d58fad. My guess would be 
>> that it's xsetbv.
>>
>> If it is then you probably want to make sure you are running hypervisor 
>> that has commit e8121c54 ("x86/xsave: enable support for new ISA 
>> extensions"). Looks like the first version that has it is 4.5 and you 
>> seem to be running 4.4.2.
>>
>> Copying Jan to see if there are plans to backport this (probably not 
>> since it's a new feature).
> 
> Hmm, if there are features getting exposed that lead to crashes like
> this, then while we wouldn't normally backport enhancements, we
> may need to consider adding a one-off patch to hide respective
> features to that stable branch. But first we of course need to
> understand what is going on here.
> 
> Jan
> 

I will try with 4.6.0 asap, unfortunately the 4.4.2 image i have is not
built with debug enabled and i'm unable to run gdb at boot, i'm building
a new one right now.
If you need anything else please be very step-specific since i'm not
very practical at this.

Thank you,
John.

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