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

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

On 02/16/2012 04:24 AM, Alexander Graf wrote:

quoted

On 16.02.2012, at 10:26, Liu Yu [off-list ref] wrote:

quoted

+_GLOBAL(epapr_ev_idle)
+epapr_ev_idle:
+    rlwinm    r3,r1,0,0,31-THREAD_SHIFT    /* current thread_info =

*/

quoted

quoted

+    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 =

*/

quoted

quoted

+
+    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

=20
Can't you just bl into epapr_hypercall_start? You don't even have to =

save the old lr. because we never return anyways :)

=20
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