[RFC PATCH 1/3] powerpc/pseries/vas: Modify reconfig open/close functions for migration

[Haren Myneni <haren@linux.ibm.com>]

VAS is a hardware engine stays on the chip. So when the partition
migrates, all VAS windows on the source system have to be closed
and reopen them on the destination after migration.

This patch make changes to the current reconfig_open/close_windows
functions to support migration:
- Sets the window status to VAS_WIN_MIGRATE_CLOSE when closes and
  reopen windows with the same status during resume.
- Continue to close all windows even if deallocate HCALL failed
  (should not happen) since no way to stop migration with the
  current LPM implementation.

Signed-off-by: Haren Myneni <haren@linux.ibm.com>
---
 arch/powerpc/include/asm/vas.h       |  2 +
 arch/powerpc/platforms/pseries/vas.c | 63 ++++++++++++++++++++++------
 2 files changed, 52 insertions(+), 13 deletions(-)

diff --git a/arch/powerpc/include/asm/vas.h b/arch/powerpc/include/asm/vas.h
index 72d1df038b4b..8b28cd7aaedc 100644
--- a/arch/powerpc/include/asm/vas.h
+++ b/arch/powerpc/include/asm/vas.h
@@ -41,6 +41,8 @@
 #define VAS_WIN_NO_CRED_CLOSE	0x4	/* Linux specific status when */
 					/* window is closed due to lost */
 					/* credit */
+#define VAS_WIN_MIGRATE_CLOSE	0x5	/* Linux status when window is */
+					/* closed due to migration */
 /*
  * Get/Set bit fields
  */
diff --git a/arch/powerpc/platforms/pseries/vas.c b/arch/powerpc/platforms/pseries/vas.c
index 169f0cccb166..b9d1c0bac624 100644
--- a/arch/powerpc/platforms/pseries/vas.c
+++ b/arch/powerpc/platforms/pseries/vas.c
@@ -449,11 +449,12 @@ static int vas_deallocate_window(struct vas_window *vwin)
 	mutex_lock(&vas_pseries_mutex);
 	/*
 	 * VAS window is already closed in the hypervisor when
-	 * lost the credit. So just remove the entry from
-	 * the list, remove task references and free vas_window
+	 * lost the credit or with migration. So just remove the entry
+	 * from the list, remove task references and free vas_window
 	 * struct.
 	 */
-	if (win->vas_win.status != VAS_WIN_NO_CRED_CLOSE) {
+	if ((win->vas_win.status != VAS_WIN_NO_CRED_CLOSE) &&
+		(win->vas_win.status != VAS_WIN_MIGRATE_CLOSE)) {
 		rc = deallocate_free_window(win);
 		if (rc) {
 			mutex_unlock(&vas_pseries_mutex);
@@ -570,12 +571,14 @@ static int get_vas_capabilities(u8 feat, enum vas_cop_feat_type type,
  * by setting the remapping to new paste address if the window is
  * active.
  */
-static int reconfig_open_windows(struct vas_caps *vcaps, int creds)
+static int reconfig_open_windows(struct vas_caps *vcaps, int creds,
+				 bool migrate)
 {
 	long domain[PLPAR_HCALL9_BUFSIZE] = {VAS_DEFAULT_DOMAIN_ID};
 	struct vas_cop_feat_caps *caps = &vcaps->caps;
 	struct pseries_vas_window *win = NULL, *tmp;
 	int rc, mv_ents = 0;
+	int status;
 
 	/*
 	 * Nothing to do if there are no closed windows.
@@ -594,8 +597,10 @@ static int reconfig_open_windows(struct vas_caps *vcaps, int creds)
 	 * (dedicated). If 1 core is added, this LPAR can have 20 more
 	 * credits. It means the kernel can reopen 20 windows. So move
 	 * 20 entries in the VAS windows lost and reopen next 20 windows.
+	 * For partition migration, reopen all windows that are closed
+	 * during resume.
 	 */
-	if (vcaps->close_wins > creds)
+	if ((vcaps->close_wins > creds) && !migrate)
 		mv_ents = vcaps->close_wins - creds;
 
 	list_for_each_entry_safe(win, tmp, &vcaps->list, win_list) {
@@ -605,11 +610,20 @@ static int reconfig_open_windows(struct vas_caps *vcaps, int creds)
 		mv_ents--;
 	}
 
+	/*
+	 * Open windows if they are closed only with migration or
+	 * DLPAR (lost credit) before.
+	 */
+	if (migrate)
+		status = VAS_WIN_MIGRATE_CLOSE;
+	else
+		status = VAS_WIN_NO_CRED_CLOSE;
+
 	list_for_each_entry_safe_from(win, tmp, &vcaps->list, win_list) {
 		/*
 		 * Nothing to do on this window if it is active.
 		 */
-		if (win->vas_win.status != VAS_WIN_NO_CRED_CLOSE)
+		if (win->vas_win.status != status)
 			continue;
 
 		rc = allocate_setup_window(win, (u64 *)&domain[0],
@@ -652,17 +666,26 @@ static int reconfig_open_windows(struct vas_caps *vcaps, int creds)
  * the user space to fall back to SW compression and manage with the
  * existing windows.
  */
-static int reconfig_close_windows(struct vas_caps *vcap, int excess_creds)
+static int reconfig_close_windows(struct vas_caps *vcap, int excess_creds,
+									bool migrate)
 {
 	struct pseries_vas_window *win, *tmp;
 	struct vas_user_win_ref *task_ref;
 	struct vm_area_struct *vma;
-	int rc = 0;
+	int rc = 0, status;
+
+	if (migrate)
+		status = VAS_WIN_MIGRATE_CLOSE;
+	else
+		status = VAS_WIN_NO_CRED_CLOSE;
 
 	list_for_each_entry_safe(win, tmp, &vcap->list, win_list) {
 		/*
 		 * This window is already closed due to lost credit
 		 * before. Go for next window.
+		 * For migration, nothing to do since this window
+		 * closed for DLPAR and will be reopened even on
+		 * the destination system with other DLPAR operation.
 		 */
 		if (win->vas_win.status == VAS_WIN_NO_CRED_CLOSE)
 			continue;
@@ -674,7 +697,7 @@ static int reconfig_close_windows(struct vas_caps *vcap, int excess_creds)
 		 * Number of available credits are reduced, So select
 		 * and close windows.
 		 */
-		win->vas_win.status = VAS_WIN_NO_CRED_CLOSE;
+		win->vas_win.status = status;
 
 		mmap_write_lock(task_ref->mm);
 		/*
@@ -697,12 +720,24 @@ static int reconfig_close_windows(struct vas_caps *vcap, int excess_creds)
 		 * later when the process issued with close(FD).
 		 */
 		rc = deallocate_free_window(win);
-		if (rc)
+		/*
+		 * This failure is from the hypervisor.
+		 * No way to stop migration for these failures.
+		 * So ignore error and continue closing other windows.
+		 */
+		if (rc && !migrate)
 			return rc;
 
 		vcap->close_wins++;
 
-		if (!--excess_creds)
+		/*
+		 * For migration, do not depend on lpar_creds in case if
+		 * mismatch with the hypervisor value (should not happen).
+		 * So close all active windows in the list and will be
+		 * reopened windows based on the new lpar_creds on the
+		 * destination system during resume.
+		 */
+		if (!migrate && !--excess_creds)
 			break;
 	}
 
@@ -757,7 +792,8 @@ int vas_reconfig_capabilties(u8 type)
 		 * target, reopen windows if they are closed due to
 		 * the previous DLPAR (core removal).
 		 */
-		rc = reconfig_open_windows(vcaps, new_creds - lpar_creds);
+		rc = reconfig_open_windows(vcaps, new_creds - lpar_creds,
+									false);
 	} else {
 		/*
 		 * # active windows is more than new LPAR available
@@ -765,7 +801,8 @@ int vas_reconfig_capabilties(u8 type)
 		 */
 		active_wins = vcaps->num_wins - vcaps->close_wins;
 		if (active_wins > new_creds)
-			rc = reconfig_close_windows(vcaps, active_wins - new_creds);
+			rc = reconfig_close_windows(vcaps, active_wins - new_creds,
+										false);
 	}
 
 out:
-- 
2.27.0