s390/kernel: Fix smp_call_ipl_cpu() for offline CPUs

If the IPL CPU is offline, currently the pcpu_delegate() function
used by smp_call_ipl_cpu() does not work because pcpu_delegate()
modifies the lowcore of the target CPU. In case of an offline
IPL CPU currently the prefix register is zero but pcpu->lowcore
still points to the old prefix page. Therefore the lowcore changes
done by pcpu_delegate() have no effect.

With this fix pcpu_delegate() now uses memcpy_absolute() and therefore
also prepares the absolute zero lowcore if the target CPU has prefix
register zero.

Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 10 insertions, 9 deletions

diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
index 9948bd09ee57..5c7bf24849b2 100644
--- a/arch/s390/kernel/smp.c
+++ b/arch/s390/kernel/smp.c
@@ -297,26 +297,27 @@ static void pcpu_start_fn(struct pcpu *pcpu, void (*func)(void *), void *data)
 static void pcpu_delegate(struct pcpu *pcpu, void (*func)(void *),
                           void *data, unsigned long stack)
 {
-        struct _lowcore *lc = pcpu->lowcore;
-        unsigned short this_cpu;
+        struct _lowcore *lc = lowcore_ptr[pcpu - pcpu_devices];
+        struct {
+                unsigned long   stack;
+                void            *func;
+                void            *data;
+                unsigned long   source;
+        } restart = { stack, func, data, stap() };
 
         __load_psw_mask(psw_kernel_bits);
-        this_cpu = stap();
-        if (pcpu->address == this_cpu)
+        if (pcpu->address == restart.source)
                 func(data);     /* should not return */
         /* Stop target cpu (if func returns this stops the current cpu). */
         pcpu_sigp_retry(pcpu, sigp_stop, 0);
         /* Restart func on the target cpu and stop the current cpu. */
-        lc->restart_stack = stack;
-        lc->restart_fn = (unsigned long) func;
-        lc->restart_data = (unsigned long) data;
-        lc->restart_source = (unsigned long) this_cpu;
+        memcpy_absolute(&lc->restart_stack, &restart, sizeof(restart));
         asm volatile(
                 "0:     sigp    0,%0,6  # sigp restart to target cpu\n"
                 "       brc     2,0b    # busy, try again\n"
                 "1:     sigp    0,%1,5  # sigp stop to current cpu\n"
                 "       brc     2,1b    # busy, try again\n"
-                : : "d" (pcpu->address), "d" (this_cpu) : "0", "1", "cc");
+                : : "d" (pcpu->address), "d" (restart.source) : "0", "1", "cc");
         for (;;) ;
 }