Commit 9327dc0a authored by Nathan Lynch's avatar Nathan Lynch Committed by Michael Ellerman

powerpc/pseries/mobility: use stop_machine for join/suspend

The partition suspend sequence as specified in the platform
architecture requires that all active processor threads call
H_JOIN, which:

- suspends the calling thread until it is the target of
  an H_PROD; or
- immediately returns H_CONTINUE, if the calling thread is the last to
  call H_JOIN. This thread is expected to call ibm,suspend-me to
  completely suspend the partition.

Upon returning from ibm,suspend-me the calling thread must wake all
others using H_PROD.

rtas_ibm_suspend_me_unsafe() uses on_each_cpu() to implement this
protocol, but because of its synchronizing nature this is susceptible
to deadlock versus users of stop_machine() or other callers of
on_each_cpu().

Not only is stop_machine() intended for use cases like this, it
handles error propagation and allows us to keep the data shared
between CPUs minimal: a single atomic counter which ensures exactly
one CPU will wake the others from their joined states.

Switch the migration code to use stop_machine() and a less complex
local implementation of the H_JOIN/ibm,suspend-me logic, which
carries additional benefits:

- more informative error reporting, appropriately ratelimited
- resets the lockup detector / watchdog on resume to prevent lockup
  warnings when the OS has been suspended for a time exceeding the
  threshold.

Fixes: 91dc182c ("[PATCH] powerpc: special-case ibm,suspend-me RTAS call")
Signed-off-by: default avatarNathan Lynch <nathanl@linux.ibm.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201207215200.1785968-13-nathanl@linux.ibm.com
parent d9213319
...@@ -12,9 +12,11 @@ ...@@ -12,9 +12,11 @@
#include <linux/cpu.h> #include <linux/cpu.h>
#include <linux/kernel.h> #include <linux/kernel.h>
#include <linux/kobject.h> #include <linux/kobject.h>
#include <linux/nmi.h>
#include <linux/sched.h> #include <linux/sched.h>
#include <linux/smp.h> #include <linux/smp.h>
#include <linux/stat.h> #include <linux/stat.h>
#include <linux/stop_machine.h>
#include <linux/completion.h> #include <linux/completion.h>
#include <linux/device.h> #include <linux/device.h>
#include <linux/delay.h> #include <linux/delay.h>
...@@ -405,6 +407,128 @@ static int wait_for_vasi_session_suspending(u64 handle) ...@@ -405,6 +407,128 @@ static int wait_for_vasi_session_suspending(u64 handle)
return ret; return ret;
} }
static void prod_single(unsigned int target_cpu)
{
long hvrc;
int hwid;
hwid = get_hard_smp_processor_id(target_cpu);
hvrc = plpar_hcall_norets(H_PROD, hwid);
if (hvrc == H_SUCCESS)
return;
pr_err_ratelimited("H_PROD of CPU %u (hwid %d) error: %ld\n",
target_cpu, hwid, hvrc);
}
static void prod_others(void)
{
unsigned int cpu;
for_each_online_cpu(cpu) {
if (cpu != smp_processor_id())
prod_single(cpu);
}
}
static u16 clamp_slb_size(void)
{
u16 prev = mmu_slb_size;
slb_set_size(SLB_MIN_SIZE);
return prev;
}
static int do_suspend(void)
{
u16 saved_slb_size;
int status;
int ret;
pr_info("calling ibm,suspend-me on CPU %i\n", smp_processor_id());
/*
* The destination processor model may have fewer SLB entries
* than the source. We reduce mmu_slb_size to a safe minimum
* before suspending in order to minimize the possibility of
* programming non-existent entries on the destination. If
* suspend fails, we restore it before returning. On success
* the OF reconfig path will update it from the new device
* tree after resuming on the destination.
*/
saved_slb_size = clamp_slb_size();
ret = rtas_ibm_suspend_me(&status);
if (ret != 0) {
pr_err("ibm,suspend-me error: %d\n", status);
slb_set_size(saved_slb_size);
}
return ret;
}
static int do_join(void *arg)
{
atomic_t *counter = arg;
long hvrc;
int ret;
/* Must ensure MSR.EE off for H_JOIN. */
hard_irq_disable();
hvrc = plpar_hcall_norets(H_JOIN);
switch (hvrc) {
case H_CONTINUE:
/*
* All other CPUs are offline or in H_JOIN. This CPU
* attempts the suspend.
*/
ret = do_suspend();
break;
case H_SUCCESS:
/*
* The suspend is complete and this cpu has received a
* prod.
*/
ret = 0;
break;
case H_BAD_MODE:
case H_HARDWARE:
default:
ret = -EIO;
pr_err_ratelimited("H_JOIN error %ld on CPU %i\n",
hvrc, smp_processor_id());
break;
}
if (atomic_inc_return(counter) == 1) {
pr_info("CPU %u waking all threads\n", smp_processor_id());
prod_others();
}
/*
* Execution may have been suspended for several seconds, so
* reset the watchdog.
*/
touch_nmi_watchdog();
return ret;
}
static int pseries_migrate_partition(u64 handle)
{
atomic_t counter = ATOMIC_INIT(0);
int ret;
ret = wait_for_vasi_session_suspending(handle);
if (ret)
return ret;
ret = stop_machine(do_join, &counter, cpu_online_mask);
if (ret == 0)
post_mobility_fixup();
return ret;
}
static ssize_t migration_store(struct class *class, static ssize_t migration_store(struct class *class,
struct class_attribute *attr, const char *buf, struct class_attribute *attr, const char *buf,
size_t count) size_t count)
...@@ -416,16 +540,10 @@ static ssize_t migration_store(struct class *class, ...@@ -416,16 +540,10 @@ static ssize_t migration_store(struct class *class,
if (rc) if (rc)
return rc; return rc;
rc = wait_for_vasi_session_suspending(streamid); rc = pseries_migrate_partition(streamid);
if (rc)
return rc;
rc = rtas_ibm_suspend_me_unsafe(streamid);
if (rc) if (rc)
return rc; return rc;
post_mobility_fixup();
return count; return count;
} }
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment