Problems with hypercalls

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 [off-list ref] wrote:

quoted

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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