Re: [PATCH v9 07/18] x86/virt/tdx: Do TDX module per-cpu initialization

Peter Zijlstra
2023-02-15T09:16:49Z

On Tue, Feb 14, 2023 at 10:53:26PM +0000, Huang, Kai wrote:

> Sure. I just tried to do. There are two minor things:
>
> 1) should I just use smp_cond_func_t directly as the cond function?

Yeah, might as well I suppose...

> 2) schedule_on_each_cpu() takes cpus_read_lock() internally. However in my
> case, tdx_enable() already takes that so I need a _locked_ version.
>
> How does below look like? (Not tested)
>
> +/**
> + * schedule_on_each_cpu_cond_locked - execute a function synchronously
> + * on each online CPU for which the
> + * condition function returns positive
> + * @func: the function to call
> + * @cond_func: the condition function to call
> + * @cond_data: the data passed to the condition function
> + *
> + * schedule_on_each_cpu_cond_locked() executes @func on each online CPU
> + * when @cond_func returns positive for that cpu, using the system
> + * workqueue and blocks until all CPUs have completed.
> + *
> + * schedule_on_each_cpu_cond_locked() doesn't hold read lock of CPU
> + * hotplug lock but depend on the caller to do.
> + *
> + * schedule_on_each_cpu_cond_locked() is very slow.
> + *
> + * Return:
> + * 0 on success, -errno on failure.
> + */
> +int schedule_on_each_cpu_cond_locked(work_func_t func,
> + smp_cond_func_t cond_func,
> + void *cond_data)
> +{
> + int cpu;
> + struct work_struct __percpu *works;
> +
> + works = alloc_percpu(struct work_struct);
> + if (!works)
> + return -ENOMEM;
> +
> + for_each_online_cpu(cpu) {
> + struct work_struct *work = per_cpu_ptr(works, cpu);
> +
> + if (cond_func && !cond_func(cpu, cond_data))
> + continue;
> +
> + INIT_WORK(work, func);
> + schedule_work_on(cpu, work);
> + }
> +
> + for_each_online_cpu(cpu)

I think you need to skip some flushes too. Given we skip setting
work->func, this will go WARN, see __flush_work().

> + flush_work(per_cpu_ptr(works, cpu));
> +
> + free_percpu(works);
> + return 0;
> +}
> +
> +/**
> + * schedule_on_each_cpu_cond - execute a function synchronously on each
> + * online CPU for which the condition
> + * function returns positive
> + * @func: the function to call
> + * @cond_func: the condition function to call
> + * @cond_data: the data passed to the condition function
> + *
> + * schedule_on_each_cpu_cond() executes @func on each online CPU
> + * when @cond_func returns positive for that cpu, using the system
> + * workqueue and blocks until all CPUs have completed.
> + *
> + * schedule_on_each_cpu_cond() is very slow.
> + *
> + * Return:
> + * 0 on success, -errno on failure.
> + */
> +int schedule_on_each_cpu_cond(work_func_t func,
> + smp_cond_func_t cond_func,
> + void *cond_data)
> +{
> + int ret;
> +
> + cpus_read_lock();
> +
> + ret = schedule_on_each_cpu_cond_locked(func, cond_func, cond_data);
> +
> + cpus_read_unlock();
> +
> + return ret;
> +}

Also, re-implement schedule_on_each_cpu() using the above to save a
bunch of duplication:

int schedule_on_each_cpu(work_func_t func)
{
return schedule_on_each_cpu_cond(func, NULL, NULL);
}

That said, I find it jarring that the schedule_on*() family doesn't have
a void* argument to the function, like the smp_*() family has. So how
about something like the below (equally untested). It preserves the
current semantics, but allows a work function to cast to schedule_work
and access ->info if it so desires.

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index a0143dd24430..5e97111322b2 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -103,6 +103,11 @@ struct work_struct {
#endif
};

+struct schedule_work {
+ struct work_struct work;
+ void *info;
+};
+
#define WORK_DATA_INIT() ATOMIC_LONG_INIT((unsigned long)WORK_STRUCT_NO_POOL)
#define WORK_DATA_STATIC_INIT() \
ATOMIC_LONG_INIT((unsigned long)(WORK_STRUCT_NO_POOL | WORK_STRUCT_STATIC))
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 07895deca271..c73bb8860bbc 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -51,6 +51,7 @@
#include <linux/sched/isolation.h>
#include <linux/nmi.h>
#include <linux/kvm_para.h>
+#include <linux/smp.h>

#include "workqueue_internal.h"

@@ -3302,43 +3303,64 @@ bool cancel_delayed_work_sync(struct delayed_work *dwork)
}
EXPORT_SYMBOL(cancel_delayed_work_sync);

-/**
- * schedule_on_each_cpu - execute a function synchronously on each online CPU
- * @func: the function to call
- *
- * schedule_on_each_cpu() executes @func on each online CPU using the
- * system workqueue and blocks until all CPUs have completed.
- * schedule_on_each_cpu() is very slow.
- *
- * Return:
- * 0 on success, -errno on failure.
- */
-int schedule_on_each_cpu(work_func_t func)
+int schedule_on_each_cpu_cond_locked(work_func_t func, smp_cond_func_t cond_func, void *info)
{
+ struct schedule_work __percpu *works;
int cpu;
- struct work_struct __percpu *works;

- works = alloc_percpu(struct work_struct);
+ works = alloc_percpu(struct schedule_work);
if (!works)
return -ENOMEM;

- cpus_read_lock();
-
for_each_online_cpu(cpu) {
- struct work_struct *work = per_cpu_ptr(works, cpu);
+ struct schedule_work *work = per_cpu_ptr(works, cpu);

- INIT_WORK(work, func);
- schedule_work_on(cpu, work);
+ if (cond_func && !cond_func(cpu, info))
+ continue;
+
+ INIT_WORK(&work->work, func);
+ work->info = info;
+ schedule_work_on(cpu, &work->work);
}

- for_each_online_cpu(cpu)
- flush_work(per_cpu_ptr(works, cpu));
+ for_each_online_cpu(cpu) {
+ struct schedule_work *work = per_cpu_ptr(works, cpu);
+
+ if (work->work.func)
+ flush_work(&work->work);
+ }

- cpus_read_unlock();
free_percpu(works);
return 0;
}

+int schedule_on_each_cpu_cond(work_func_t func, smp_cond_func_t cond_func, void *info)
+{
+ int ret;
+
+ cpus_read_lock();
+ ret = schedule_on_each_cpu_cond_locked(func, cond, info);
+ cpus_read_unlock();
+
+ return ret;
+}
+
+/**
+ * schedule_on_each_cpu - execute a function synchronously on each online CPU
+ * @func: the function to call
+ *
+ * schedule_on_each_cpu() executes @func on each online CPU using the
+ * system workqueue and blocks until all CPUs have completed.
+ * schedule_on_each_cpu() is very slow.
+ *
+ * Return:
+ * 0 on success, -errno on failure.
+ */
+int schedule_on_each_cpu(work_func_t func)
+{
+ return schedule_on_each_cpu_cond(func, NULL, NULL);
+}
+
/**
* execute_in_process_context - reliably execute the routine with user context
* @fn: the function to execute