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References: <201509241626.33410.wpaul@windriver.com>
From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <560C1668.3080200@redhat.com>
Date: Wed, 30 Sep 2015 19:05:44 +0200
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Subject: Re: [Qemu-devel] Possible bug in target-i386/helper.c:do_cpu_init()?
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To: Bill Paul <wpaul@windriver.com>, qemu-devel@nongnu.org
Cc: Eduardo Habkost <ehabkost@redhat.com>, Richard Henderson <rth@twiddle.net>



On 25/09/2015 01:26, Bill Paul wrote:
> The result of this is that if the CPU was in long mode and you do an INIT IPI, 
> the CPU still has the EFER.LMA and EFER.LME bits set, even though it's not 
> actually running in long mode anymore. It doesn't seem possible for the guest 
> to get the CPU out of this state, and one nasty side-effect is that trying to 
> set the CR0 to enable paging never succeeds.
> 
> I added the following code at line 1240 above as a workaround:
> 
> #ifdef TARGET_X86_64
>     /*
>      * The initial state of the CPU is not 64-bit mode. This being
>      * the case, don't leave the EFER.LME or EFER.LME bits set.
>      */
>  
>     cpu_load_efer(env, 0);
> #endif
> 
> This seemed to fix the problem I was having, however I'm not certain this is 
> the correct fix.

I think a better fix is to move the "uint64_t efer;" field to some place
before the dummy "struct {} start_init_save;" marker in
target-i386/cpu.h.  Can you test it and send a patch if it works?

Thanks,

Paolo