Problems with hypercalls

[emilie lefebvre]

Hi, 

I try this :


 local_irq_save(flags);

 kvm_hypercall2 ( 6, 2, 2);

 local_irq_restore(flags);



But I still have my kernel panic with  "divide error: 0000 [#1] SMP" that I don't understand!

with or without lock, nothing change, the same when I change the current state.



I tried to move my hypercall and I still don't understand why it works just before my test

"if (piga_on == 1)" without any protections (like disable interrupts) and not after..



 Thank you for trying to help me


> Date: Thu, 9 Jun 2011 09:46:12 +0800
> Subject: Re: Problems with hypercalls
> From: htmldeveloper at gmail.com
> To: tricheurs at hotmail.fr
> CC: kernelnewbies at kernelnewbies.org
> 
> perhaps this example will provide u with more info:
> 
> http://a380.informatik.uni-bremen.de/lxr/source/arch/x86/lguest/boot.c
> 
> I think the correct step is to disable IRQ instead - before every call
> to kvm_hypercallX().   The reason is given in the remark:
> 
> 110         /*
> 111          * Disable interrupts if not already disabled: we don't want an
> 112          * interrupt handler making a hypercall while we're already doing
> 113          * one!
> 114          */
> 
> On Wed, Jun 8, 2011 at 10:54 PM, emilie lefebvre <tricheurs at hotmail.fr> wrote:
> >
> > This is my function :
> >
> > static spinlock_t xgr_learn_lock = SPIN_LOCK_UNLOCKED;
> > static int piga_seq_cpt = 1;
> >
> > /*
> > * Function called for each systemcall (Hook SELinux avc function)
> > */
> > int piga_control(u32 ssid, ...., struct av_decision * avd) {
> >
> > /*
> > * Here my hypercall work but block my vm with this error :
> > *                " BUG: scheduling while atomic ... "
> > */
> >
> > spin_lock_bh(&xgr_learn_lock);
> >   if ( in_atomic())
> >            kvm_hypercall2 ( 6, (unsigned long)2 ,(unsigned
> > long)piga_seq_cpt);
> >   spin_unlock_bh(&xgr_learn_lock);
> >
> >  if (piga_on == 1) {
> > /*
> > * Here my hypercall make a kernel panic with this error:
> > *             " divide error: 0000 [#1] SMP"
> > */
> >                 spin_lock_bh(&xgr_learn_lock);
> >                 set_current_state(TASK_UNINTERRUPTIBLE);
> >                 kvm_hypercall2 ( 6, (unsigned long)2 ,(unsigned
> > long)piga_seq_cpt);
> >                 set_current_state(TASK_RUNNING);
> >                 spin_lock_bh(&xgr_learn_lock);
> > }
> > }
> >
> >
> 
> I think u generally set TASK_UNINTERRUPTIBLE whenever about to modify
> the scheduling task list (eg, wait queue manipulation) or about to
> call "schedule()" (ie, doing your own scheduling).   The function
> set_current_state() literally just set the variable value only, it
> does not disable interrupt.
> 
> -- 
> Regards,
> Peter Teoh
> 
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