[PATCH v3] powerpc/pseries/vas: Migration suspend waits for no in-progress open windows
Haren Myneni
haren at linux.ibm.com
Fri Oct 20 11:44:24 AEDT 2023
The hypervisor returns migration failure if all VAS windows are not
closed. During pre-migration stage, vas_migration_handler() sets
migration_in_progress flag and closes all windows from the list.
The allocate VAS window routine checks the migration flag, setup
the window and then add it to the list. So there is possibility of
the migration handler missing the window that is still in the
process of setup.
t1: Allocate and open VAS t2: Migration event
window
lock vas_pseries_mutex
If migration_in_progress set
unlock vas_pseries_mutex
return
open window HCALL
unlock vas_pseries_mutex
Modify window HCALL lock vas_pseries_mutex
setup window migration_in_progress=true
Closes all windows from
the list
unlock vas_pseries_mutex
lock vas_pseries_mutex return
if nr_closed_windows == 0
// No DLPAR CPU or migration
add to the list
unlock vas_pseries_mutex
return
unlock vas_pseries_mutex
Close VAS window
// due to DLPAR CPU or migration
return -EBUSY
This patch resolves the issue with the following steps:
- Set the migration_in_progress flag without holding mutex.
- Introduce nr_open_wins_progress counter in VAS capabilities
struct
- This counter tracks the number of open windows are still in
progress
- The allocate setup window thread closes windows if the migration
is set and decrements nr_open_window_progress counter
- The migration handler waits for no in-progress open windows.
Fixes: 37e6764895ef ("powerpc/pseries/vas: Add VAS migration handler")
Signed-off-by: Haren Myneni <haren at linux.ibm.com>
---
v1 -> v2:
- Do not define the migration_in_progress flag as atomic as
suggested by Nathan
v2 -> v3:
- Use wait_event() instead of wait_event_interruptible() so that
returns after all windows are closed as suggested by Nathan
---
arch/powerpc/platforms/pseries/vas.c | 45 +++++++++++++++++++++++-----
arch/powerpc/platforms/pseries/vas.h | 2 ++
2 files changed, 40 insertions(+), 7 deletions(-)
diff --git a/arch/powerpc/platforms/pseries/vas.c b/arch/powerpc/platforms/pseries/vas.c
index 88bee56ff92b..c2c6cc2b22ea 100644
--- a/arch/powerpc/platforms/pseries/vas.c
+++ b/arch/powerpc/platforms/pseries/vas.c
@@ -32,6 +32,7 @@ static struct hv_vas_cop_feat_caps hv_cop_caps;
static struct vas_caps vascaps[VAS_MAX_FEAT_TYPE];
static DEFINE_MUTEX(vas_pseries_mutex);
static bool migration_in_progress;
+static DECLARE_WAIT_QUEUE_HEAD(open_win_progress_wq);
static long hcall_return_busy_check(long rc)
{
@@ -384,11 +385,15 @@ static struct vas_window *vas_allocate_window(int vas_id, u64 flags,
* same fault IRQ is not freed by the OS before.
*/
mutex_lock(&vas_pseries_mutex);
- if (migration_in_progress)
+ if (migration_in_progress) {
rc = -EBUSY;
- else
+ } else {
rc = allocate_setup_window(txwin, (u64 *)&domain[0],
cop_feat_caps->win_type);
+ if (!rc)
+ atomic_inc(&caps->nr_open_wins_progress);
+ }
+
mutex_unlock(&vas_pseries_mutex);
if (rc)
goto out;
@@ -403,8 +408,17 @@ static struct vas_window *vas_allocate_window(int vas_id, u64 flags,
goto out_free;
txwin->win_type = cop_feat_caps->win_type;
- mutex_lock(&vas_pseries_mutex);
+
/*
+ * The migration SUSPEND thread sets migration_in_progress and
+ * closes all open windows from the list. But the window is
+ * added to the list after open and modify HCALLs. So possible
+ * that migration_in_progress is set before modify HCALL which
+ * may cause some windows are still open when the hypervisor
+ * initiates the migration.
+ * So checks the migration_in_progress flag again and close all
+ * open windows.
+ *
* Possible to lose the acquired credit with DLPAR core
* removal after the window is opened. So if there are any
* closed windows (means with lost credits), do not give new
@@ -412,9 +426,11 @@ static struct vas_window *vas_allocate_window(int vas_id, u64 flags,
* after the existing windows are reopened when credits are
* available.
*/
- if (!caps->nr_close_wins) {
+ mutex_lock(&vas_pseries_mutex);
+ if (!caps->nr_close_wins && !migration_in_progress) {
list_add(&txwin->win_list, &caps->list);
caps->nr_open_windows++;
+ atomic_dec(&caps->nr_open_wins_progress);
mutex_unlock(&vas_pseries_mutex);
vas_user_win_add_mm_context(&txwin->vas_win.task_ref);
return &txwin->vas_win;
@@ -432,6 +448,8 @@ static struct vas_window *vas_allocate_window(int vas_id, u64 flags,
*/
free_irq_setup(txwin);
h_deallocate_vas_window(txwin->vas_win.winid);
+ if (atomic_dec_return(&caps->nr_open_wins_progress) == 0)
+ wake_up(&open_win_progress_wq);
out:
atomic_dec(&cop_feat_caps->nr_used_credits);
kfree(txwin);
@@ -931,14 +949,14 @@ int vas_migration_handler(int action)
struct vas_caps *vcaps;
int i, rc = 0;
+ pr_info("VAS migration event %d\n", action);
+
/*
* NX-GZIP is not enabled. Nothing to do for migration.
*/
if (!copypaste_feat)
return rc;
- mutex_lock(&vas_pseries_mutex);
-
if (action == VAS_SUSPEND)
migration_in_progress = true;
else
@@ -984,12 +1002,24 @@ int vas_migration_handler(int action)
switch (action) {
case VAS_SUSPEND:
+ mutex_lock(&vas_pseries_mutex);
rc = reconfig_close_windows(vcaps, vcaps->nr_open_windows,
true);
+ mutex_unlock(&vas_pseries_mutex);
+ /*
+ * Windows are included in the list after successful
+ * open. So wait for closing these in-progress open
+ * windows in vas_allocate_window() which will be
+ * done if the migration_in_progress is set.
+ */
+ wait_event(open_win_progress_wq,
+ !atomic_read(&vcaps->nr_open_wins_progress));
break;
case VAS_RESUME:
+ mutex_lock(&vas_pseries_mutex);
atomic_set(&caps->nr_total_credits, new_nr_creds);
rc = reconfig_open_windows(vcaps, new_nr_creds, true);
+ mutex_unlock(&vas_pseries_mutex);
break;
default:
/* should not happen */
@@ -1005,8 +1035,9 @@ int vas_migration_handler(int action)
goto out;
}
+ pr_info("VAS migration event (%d) successful\n", action);
+
out:
- mutex_unlock(&vas_pseries_mutex);
return rc;
}
diff --git a/arch/powerpc/platforms/pseries/vas.h b/arch/powerpc/platforms/pseries/vas.h
index 7115043ec488..35e899f2ee20 100644
--- a/arch/powerpc/platforms/pseries/vas.h
+++ b/arch/powerpc/platforms/pseries/vas.h
@@ -91,6 +91,8 @@ struct vas_cop_feat_caps {
struct vas_caps {
struct vas_cop_feat_caps caps;
struct list_head list; /* List of open windows */
+ atomic_t nr_open_wins_progress; /* Number of open windows in */
+ /* progress. Used in migration */
int nr_close_wins; /* closed windows in the hypervisor for DLPAR */
int nr_open_windows; /* Number of successful open windows */
u8 feat; /* Feature type */
--
2.26.3
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