[XenARM] [MINIOS] evtchn_pending_sel issue

[ROSSIER Daniel <Daniel.Rossier@xxxxxxxxxx>]

Hi Folks,

 

Can anybody help us in the following problem:

(still working on embeddedXEN with ARM core)

 

we're trying to use miniOS (basically the same than x86 version) and we face a strange issue regarding

the hypervisor callback. Here is a portion of code:

…

 

#define active_evtchns(cpu,sh,idx)              \

    ((sh)->evtchn_pending[idx] &                \

     ~(sh)->evtchn_mask[idx])

 

…

l1 = xchg(&vcpu_info->evtchn_pending_sel, 0);

        while (l1 != 0) {

                l1i = __ffs(l1);

                l1 &= ~(1 << l1i);

                while ((l2 = active_evtchns(cpu, s, l1i)) != 0) {

                        l2i = __ffs(l2);

                        l2 &= ~(1 << l2i);

 

                        port = (l1i << 5) + l2i;

                        do_event(port, regs);

                }

        }

 

The timer init function bind the VIRQ_TIMER to a specific handler, ok. VIRQ_TIMER is equal to 0 and therefore, the bit 0 of

evtchn_pending and evtchn_mask are set correctly (checked). However, the code above tells us that l1i is set to 1 (and not 0).

Consequently, we never statisfy the second while() condition.

 

It seems that there is a shift of one bit in the computation of l1i, since _ffs return 1 for the least significant bit (and not 0).

What do you think?

 

What I'm wondering is how it could work .. (and probably it could ;-) just something that probably I missed….

 

Thanks for your help

 

Daniel

 

 

 

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