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Re: [PATCH v4 3/3] KVM: PPC: epapr: install ev_idle hcall for e500 guest

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On 16.02.2012, at 17:58, Scott Wood wrote:

> On 02/16/2012 04:24 AM, Alexander Graf wrote:
>> On 16.02.2012, at 10:26, Liu Yu <yu.liu@xxxxxxxxxxxxx> wrote:
>>> +_GLOBAL(epapr_ev_idle)
>>> +epapr_ev_idle:
>>> +    rlwinm    r3,r1,0,0,31-THREAD_SHIFT    /* current thread_info */
>>> +    lwz    r4,TI_LOCAL_FLAGS(r3)    /* set napping bit */
>>> +    ori    r4,r4,_TLF_NAPPING    /* so when we take an exception */
>>> +    stw    r4,TI_LOCAL_FLAGS(r3)    /* it will return to our caller */
>>> +
>>> +    wrteei    1
>>> +
>>> +idle_loop:
>>> +    LOAD_REG_IMMEDIATE(r11, HC_VENDOR_EPAPR | HC_EV_IDLE)
>>> +
>>> +.global epapr_ev_idle_start
>>> +epapr_ev_idle_start:
>>> +    li    r3, -1
>>> +    nop
>>> +    nop
>>> +    nop
>> 
>> Can't you just bl into epapr_hypercall_start? You don't even have to save the old lr. because we never return anyways :)
> 
> The interrupt will branch to LR, so no, we can't trash it or put it
> anywhere else.

Hrm. But we can clobber ctr, right? So how about we make the generic version do a bctr and then just do a small C wrapper that takes lr, moves it to ctr and branches to the generic one?

Then we don't have to replicate the hypercall code all over again for every invocation.

Alex

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