s390/smp: ensure global control register contents are in sync

Globally setting a bit in control registers is done with
smp_ctl_set_clear_bit(). This is using on_each_cpu() to execute a function
which actually sets the control register bit on each online CPU. This can
be problematic since on_each_cpu() does not prevent that new CPUs come
online while it is executed, which in turn means that control register
updates could be missing on new CPUs.

In order to prevent this problem make sure that global control register
contents cannot change until new CPUs have initialized their control
registers, and marked themselves online, so they are included in subsequent
on_each_cpu() calls.

Reviewed-by: Sven Schnelle <svens@linux.ibm.com>
Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
index 9244130721d6f3214b3e37b06d2b0e08ce4dcbe2..a4edb7ea66ea763d9090844446b2a2d7566d74ef 100644 (file)
--- a/arch/s390/kernel/smp.c
+++ b/arch/s390/kernel/smp.c
@@ -253,8 +253,9 @@ static void pcpu_free_lowcore(struct pcpu *pcpu)
 
 static void pcpu_prepare_secondary(struct pcpu *pcpu, int cpu)
 {
-       struct lowcore *lc = lowcore_ptr[cpu];
+       struct lowcore *lc, *abs_lc;
 
+       lc = lowcore_ptr[cpu];
        cpumask_set_cpu(cpu, &init_mm.context.cpu_attach_mask);
        cpumask_set_cpu(cpu, mm_cpumask(&init_mm));
        lc->cpu_nr = cpu;
@@ -267,7 +268,9 @@ static void pcpu_prepare_secondary(struct pcpu *pcpu, int cpu)
        lc->machine_flags = S390_lowcore.machine_flags;
        lc->user_timer = lc->system_timer =
                lc->steal_timer = lc->avg_steal_timer = 0;
-       __ctl_store(lc->cregs_save_area, 0, 15);
+       abs_lc = get_abs_lowcore();
+       memcpy(lc->cregs_save_area, abs_lc->cregs_save_area, sizeof(lc->cregs_save_area));
+       put_abs_lowcore(abs_lc);
        lc->cregs_save_area[1] = lc->kernel_asce;
        lc->cregs_save_area[7] = lc->user_asce;
        save_access_regs((unsigned int *) lc->access_regs_save_area);
@@ -607,8 +610,8 @@ void smp_ctl_set_clear_bit(int cr, int bit, bool set)
        ctlreg = (ctlreg & parms.andval) | parms.orval;
        abs_lc->cregs_save_area[cr] = ctlreg;
        put_abs_lowcore(abs_lc);
-       spin_unlock(&ctl_lock);
        on_each_cpu(smp_ctl_bit_callback, &parms, 1);
+       spin_unlock(&ctl_lock);
 }
 EXPORT_SYMBOL(smp_ctl_set_clear_bit);
 
@@ -928,12 +931,18 @@ int __cpu_up(unsigned int cpu, struct task_struct *tidle)
        rc = pcpu_alloc_lowcore(pcpu, cpu);
        if (rc)
                return rc;
+       /*
+        * Make sure global control register contents do not change
+        * until new CPU has initialized control registers.
+        */
+       spin_lock(&ctl_lock);
        pcpu_prepare_secondary(pcpu, cpu);
        pcpu_attach_task(pcpu, tidle);
        pcpu_start_fn(pcpu, smp_start_secondary, NULL);
        /* Wait until cpu puts itself in the online & active maps */
        while (!cpu_online(cpu))
                cpu_relax();
+       spin_unlock(&ctl_lock);
        return 0;
 }