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

[Jan Kiszka <jan.kiszka@siemens.com>]

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?

Jan

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