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Date: Thu, 13 Feb 2014 07:39:54 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Fengguang Wu <fengguang.wu@intel.com>, kvm <kvm@vger.kernel.org>
CC: LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [qemu64,+smep,+smap] Kernel panic - not syncing: No working init
 found.
References: <20140213124550.GA30497@localhost> <52FCDCE5.4010301@zytor.com>
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On 02/13/2014 06:55 AM, H. Peter Anvin wrote:
> On 02/13/2014 04:45 AM, Fengguang Wu wrote:
>> Greetings,
>>
>> I find that when running
>>
>>         qemu-system-x86_64 -cpu qemu64,+smep,+smap
>>
>> Some kernels will 100% produce this error, where the error code
>> -13,-14 are -EACCES and -EFAULT:
>>
>> Any ideas?
>>
> 
> I notice this is a non-SMAP kernel:
> 
> # CONFIG_X86_SMAP is not set
> 
> If the kernel turns on SMAP in CR4 even though SMAP isn't enabled in the
> kernel, that is a kernel bug.  If Qemu enforces SMAP even if it is
> turned off in CR4, that would be a Qemu bug.  I have reproduced the
> failure locally and an am considering both possibilities now.
> 

So we do turn on the bit in CR4 even with SMAP compiled out.  This is a
bug.  However, I still get the same failure even with that bug fixed
(and qemu "info registers" verify that it is, indeed, not set) so I'm
wondering if there is a bug in Qemu as well.  However, staring at the
code in Qemu I don't see where that bug would be...

	-hpa