[Xen-devel] [PATCH v6 3/6] smp: add function to execute a function synchronously on a cpu

[Juergen Gross <jgross@xxxxxxxx>]

On some hardware models (e.g. Dell Studio 1555 laptop) some hardware
related functions (e.g. SMIs) are to be executed on physical cpu 0
only. Instead of open coding such a functionality multiple times in
the kernel add a service function for this purpose. This will enable
the possibility to take special measures in virtualized environments
like Xen, too.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
V5: rename and reshuffle parameters of smp_call_on_cpu() as requested by
    Peter Zijlstra
    test target cpu to be online as requested by Peter Zijlstra

V4: change return value in case of illegal cpu as requested by Peter Zijlstra
    make pinning of vcpu an option as suggested by Peter Zijlstra

V2: instead of manipulating the allowed set of cpus use cpu specific
    workqueue as requested by Peter Zijlstra
---
 include/linux/smp.h |  3 +++
 kernel/smp.c        | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
 kernel/up.c         | 17 +++++++++++++++++
 3 files changed, 70 insertions(+)

diff --git a/include/linux/smp.h b/include/linux/smp.h
index eccae469..8e0cb7a 100644
--- a/include/linux/smp.h
+++ b/include/linux/smp.h
@@ -196,6 +196,9 @@ extern void arch_enable_nonboot_cpus_end(void);
 
 void smp_setup_processor_id(void);
 
+int smp_call_on_cpu(unsigned int cpu, int (*func)(void *), void *par,
+                   bool phys);
+
 /* SMP core functions */
 int smpcfd_prepare_cpu(unsigned int cpu);
 int smpcfd_dead_cpu(unsigned int cpu);
diff --git a/kernel/smp.c b/kernel/smp.c
index 4274ca5..f4f6137 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -725,3 +725,53 @@ void wake_up_all_idle_cpus(void)
        preempt_enable();
 }
 EXPORT_SYMBOL_GPL(wake_up_all_idle_cpus);
+
+/**
+ * smp_call_on_cpu - Call a function on a specific cpu
+ *
+ * Used to call a function on a specific cpu and wait for it to return.
+ * Optionally make sure the call is done on a specified physical cpu via vcpu
+ * pinning in order to support virtualized environments.
+ */
+struct smp_call_on_cpu_struct {
+       struct work_struct      work;
+       struct completion       done;
+       int                     (*func)(void *);
+       void                    *data;
+       int                     ret;
+       int                     cpu;
+};
+
+static void smp_call_on_cpu_callback(struct work_struct *work)
+{
+       struct smp_call_on_cpu_struct *sscs;
+
+       sscs = container_of(work, struct smp_call_on_cpu_struct, work);
+       if (sscs->cpu >= 0)
+               hypervisor_pin_vcpu(sscs->cpu);
+       sscs->ret = sscs->func(sscs->data);
+       if (sscs->cpu >= 0)
+               hypervisor_pin_vcpu(-1);
+
+       complete(&sscs->done);
+}
+
+int smp_call_on_cpu(unsigned int cpu, int (*func)(void *), void *par, bool 
phys)
+{
+       struct smp_call_on_cpu_struct sscs = {
+               .work = __WORK_INITIALIZER(sscs.work, smp_call_on_cpu_callback),
+               .done = COMPLETION_INITIALIZER_ONSTACK(sscs.done),
+               .func = func,
+               .data = par,
+               .cpu  = phys ? cpu : -1,
+       };
+
+       if (cpu >= nr_cpu_ids || !cpu_online(cpu))
+               return -ENXIO;
+
+       queue_work_on(cpu, system_wq, &sscs.work);
+       wait_for_completion(&sscs.done);
+
+       return sscs.ret;
+}
+EXPORT_SYMBOL_GPL(smp_call_on_cpu);
diff --git a/kernel/up.c b/kernel/up.c
index 3ccee2b..ee81ac9 100644
--- a/kernel/up.c
+++ b/kernel/up.c
@@ -83,3 +83,20 @@ void on_each_cpu_cond(bool (*cond_func)(int cpu, void *info),
        preempt_enable();
 }
 EXPORT_SYMBOL(on_each_cpu_cond);
+
+int smp_call_on_cpu(unsigned int cpu, int (*func)(void *), void *par, bool 
phys)
+{
+       int ret;
+
+       if (cpu != 0)
+               return -ENXIO;
+
+       if (phys)
+               hypervisor_pin_vcpu(0);
+       ret = func(par);
+       if (phys)
+               hypervisor_pin_vcpu(-1);
+
+       return ret;
+}
+EXPORT_SYMBOL_GPL(smp_call_on_cpu);
-- 
2.6.6


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