On Mon, 4 May 2015 13:40:20 +0200
Jiri Slaby <jslaby@xxxxxxx> wrote:
> This means:
> * add a per-thread flag to indicate whether a task is in the old or in
> the new universe,
> * reset it in _slow_ paths of syscall's entry/exit,
> * add helpers around the flag to sched.h,
> * export the status in /proc/<pid>/kgr_in_progress,
> @@ -217,6 +226,7 @@ ENTRY(system_call)
> mvc __PT_INT_CODE(4,%r11),__LC_SVC_ILC
> stg %r14,__PT_FLAGS(%r11)
> .Lsysc_do_svc:
> + HANDLE_KGRAFT %r12
> lg %r10,__TI_sysc_table(%r12) # address of system call table
> llgh %r8,__PT_INT_CODE+2(%r11)
> slag %r8,%r8,2 # shift and test for svc 0
This is not the slow path, .Lsysc_do_svc is on the main svc path. It is
"only" two instruction but nevertheless this should be avoided.
One way is to combine it with the _TIF_TRACE mechanics:
.Lsysc_nr_ok:
xc __SF_BACKCHAIN(8,%r15),__SF_BACKCHAIN(%r15)
stg %r2,__PT_ORIG_GPR2(%r11)
stg %r7,STACK_FRAME_OVERHEAD(%r15)
lgf %r9,0(%r8,%r10) # get system call add.
-> tm __TI_flags+6(%r12),_TIF_TRACE>>8
-> jnz .Lsysc_tracesys
basr %r14,%r9 # call sys_xxxx
stg %r2,__PT_R2(%r11) # store return value
Add _TIF_KGR_IN_PROGRESS to _TIF_TRACE and branch to a new label,
e.g. to .Lsysc_trace. Distinguish between _TIF_KGR_IN_PROGRESS and
the other trace reasons and either call s390_handle_kgraft or
do_syscall_trace_enter / do_syscall_trace_exit.
The same for the exit work, add _TIF_KGR_IN_PROGRESS to _TIF_WORK
and sort out the reason in .Lsysc_work. That avoids another two
instructions on the main system call path.
--
blue skies,
Martin.
"Reality continues to ruin my life." - Calvin.
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