[Qemu-devel] Re: [PATCH] Resend: x86: Reboot CPU on triple fault

[Alexander Graf <agraf@suse.de>]

On 12.01.2009, at 13:14, Jan Kiszka <jan.kiszka@siemens.com> wrote:

> lkundrak@v3.sk wrote:
>> This is a (slightly adjusted for 2009-01-04 SVN) resend of Jan  
>> Kiszka's
>> Reboot CPU on triple fault patch (see patch file for the exact  
>> reference)
>>
>> It seems like a consensus was reached on how to deal with tripple  
>> faults,
>> but noone commited the last version (8) of the patch anyways.
>>
>> Just for the record -- 386BSD relies on this behavior to reset the  
>> CPU --
>> it unmaps the whole address space in order to trigger a tripple  
>> fault.
>>
>
> Good that you picked this up! It is still on my to-do list to get this
> in, but with medium prio. However, let's try to push it a bit.
>
>> This is a slightly adjusted (for 2009-01-04 SVN) "reset on tripple  
>> fault patch"
>>
>> Originally from:
>>
>> Subject: [Qemu-devel] Re: [PATCH] x86: Reboot CPU on triple fault -  
>> Version 8
>> Message-ID: <483C340E.1030207@siemens.com>
>> Date: Tue, 27 May 2008 18:17:18 +0200
>> From: Jan Kiszka <jan.kiszka@siemens.com>
>
> Note that I posted an enhanced version on 2008-09-02, also covering
> reset logging for non-x86 archs. Please use that one.
>
> ...
>> Index: target-i386/op_helper.c
>> ===================================================================
>> --- target-i386/op_helper.c    (revision 6159)
>> +++ target-i386/op_helper.c    (working copy)
>> @@ -1244,6 +1244,9 @@
>>     }
>> }
>>
>> +/* This should come from sysemu.h - if we could include it here...  
>> */
>> +void qemu_system_reset_request(void);
>> +
>> /*
>>  * Check nested exceptions and change to double or triple fault if
>>  * needed. It should only be called, if this is not an interrupt.
>> @@ -1261,9 +1264,19 @@
>>         fprintf(logfile, "check_exception old: 0x%x new 0x%x\n",
>>                 env->old_exception, intno);
>>
>> -    if (env->old_exception == EXCP08_DBLE)
>> -        cpu_abort(env, "triple fault");
>> +#if !defined(CONFIG_USER_ONLY)
>> +    if (env->old_exception == EXCP08_DBLE) {
>> +        if (env->intercept)
>> +            helper_vmexit(SVM_EXIT_SHUTDOWN, 0);
>>
>> +        if (loglevel & CPU_LOG_RESET)
>> +            fprintf(logfile, "Triple fault\n");
>> +
>> +        qemu_system_reset_request();
>> +        return EXCP_HLT;
>> +    }
>> +#endif
>> +
>>     if ((first_contributory && second_contributory)
>>         || (env->old_exception == EXCP0E_PAGE &&
>>             (second_contributory || (intno == EXCP0E_PAGE)))) {
>
> I meanwhile think that SVM hook should rather look like this
>
> helper_svm_check_intercept_param(SVM_EXIT_SHUTDOWN, 0);
>
>
> in order to properly check if shutdown events are actually  
> intercepted.
> Alexander, am I right?

Yes, sounds right. Any reason not to put the intercept in  
reset_request? (asking blindly, I don't have access to the qemu source  
right now)

Alex

>
>
> Jan
>
> -- 
> Siemens AG, Corporate Technology, CT SE 26
> Corporate Competence Center Embedded Linux