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

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Date:	Tue, 20 Oct 2015 03:51:52 -0600
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"John Doe" <securef33d@...il.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 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

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