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

From: Alexander Graf
Subject: [Qemu-devel] Re: [PATCH] Resend: x86: Reboot CPU on triple fault
Date: Mon, 12 Jan 2009 17:41:43 +0100

On 12.01.2009, at 17:05, Jan Kiszka <address@hidden> wrote:

Alexander Graf wrote:

On 12.01.2009, at 13:14, Jan Kiszka <address@hidden> wrote:

address@hidden 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

It seems like a consensus was reached on how to deal with tripple
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: <address@hidden>
Date: Tue, 27 May 2008 18:17:18 +0200
From: Jan Kiszka <address@hidden>

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;
+    }
   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)

You mean qemu_system_reset_request? That's generic code while the hook
is x86-specific.

Sounds like the right place then. :-)



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