On Mon, 2025-08-25 at 14:10 +0530, Mahesh J Salgaonkar wrote:

On 2025-08-12 15:57:13 Tue, Haren Myneni wrote:

quoted

The hypervisor assigns one pipe per partition for all sources and
assigns new pipe after migration. Also the partition ID that is
used by source as its target ID may be changed after the migration.
So disable hvpipe during SUSPEND event with ‘hvpipe enable’ system
parameter value = 0 and enable it after migration during RESUME
event with  hvpipe enable’ system parameter value = 1.

The user space calls such as ioctl()/ read() / write() / poll()
returns  -ENXIO between SUSPEND and RESUME events. The user space
process can close FD and reestablish connection with new FD after
migration if needed (Example: source IDs are changed).

Signed-off-by: Haren Myneni <haren@linux.ibm.com>
---
 arch/powerpc/platforms/pseries/mobility.c    |  3 +
 arch/powerpc/platforms/pseries/papr-hvpipe.c | 64
++++++++++++++++++++
 arch/powerpc/platforms/pseries/papr-hvpipe.h |  6 ++
 3 files changed, 73 insertions(+)

diff --git a/arch/powerpc/platforms/pseries/mobility.c

b/arch/powerpc/platforms/pseries/mobility.c
index 62bd8e2d5d4c..95fe802ccdfd 100644

--- a/arch/powerpc/platforms/pseries/mobility.c
+++ b/arch/powerpc/platforms/pseries/mobility.c

@@ -28,6 +28,7 @@

 #include <asm/rtas.h>
 #include "pseries.h"
 #include "vas.h"	/* vas_migration_handler() */
+#include "papr-hvpipe.h"	/* hvpipe_migration_handler() */
 #include "../../kernel/cacheinfo.h"
 
 static struct kobject *mobility_kobj;

@@ -744,6 +745,7 @@ static int pseries_migrate_partition(u64

handle)
 	 * by closing VAS windows at the beginning of this
function.
 	 */
 	vas_migration_handler(VAS_SUSPEND);
+	hvpipe_migration_handler(HVPIPE_SUSPEND);
 
 	ret = wait_for_vasi_session_suspending(handle);
 	if (ret)

@@ -770,6 +772,7 @@ static int pseries_migrate_partition(u64

handle)
 
 out:
 	vas_migration_handler(VAS_RESUME);
+	hvpipe_migration_handler(HVPIPE_RESUME);
 
 	return ret;
 }

diff --git a/arch/powerpc/platforms/pseries/papr-hvpipe.c

b/arch/powerpc/platforms/pseries/papr-hvpipe.c
index bc3d1f0b4491..0edc1a29d64d 100644

--- a/arch/powerpc/platforms/pseries/papr-hvpipe.c
+++ b/arch/powerpc/platforms/pseries/papr-hvpipe.c

@@ -27,6 +27,7 @@ static unsigned char

hvpipe_ras_buf[RTAS_ERROR_LOG_MAX];
 static struct workqueue_struct *papr_hvpipe_wq;
 static struct work_struct *papr_hvpipe_work = NULL;
 static int hvpipe_check_exception_token;
+static bool hvpipe_feature;
 
 /*
  * New PowerPC FW provides support for partitions and various

@@ -233,6 +234,12 @@ static ssize_t papr_hvpipe_handle_write(struct

file *file,
 	unsigned long ret, len;
 	char *area_buf;
 
+	/*
+	 * Return -ENXIO during migration
+	 */
+	if (!hvpipe_feature)
+		return -ENXIO;
+
 	if (!src_info)
 		return -EIO;
 

@@ -325,6 +332,12 @@ static ssize_t papr_hvpipe_handle_read(struct

file *file,
 	struct papr_hvpipe_hdr hdr;
 	long ret;
 
+	/*
+	 * Return -ENXIO during migration
+	 */
+	if (!hvpipe_feature)
+		return -ENXIO;
+
 	if (!src_info)
 		return -EIO;
 

@@ -401,6 +414,12 @@ static unsigned int

papr_hvpipe_handle_poll(struct file *filp,
 {
 	struct hvpipe_source_info *src_info = filp->private_data;
 
+	/*
+	 * Return -ENXIO during migration
+	 */
+	if (!hvpipe_feature)
+		return -ENXIO;
+
 	if (!src_info)
 		return -EIO;
 

@@ -530,6 +549,12 @@ static long papr_hvpipe_dev_ioctl(struct file

*filp, unsigned int ioctl,
 	u32 srcID;
 	long ret;
 
+	/*
+	 * Return -ENXIO during migration
+	 */
+	if (!hvpipe_feature)
+		return -ENXIO;
+
 	if (get_user(srcID, argp))
 		return -EFAULT;
 

@@ -688,6 +713,44 @@ static int __init enable_hvpipe_IRQ(void)

 	return 0;
 }
 
+void hvpipe_migration_handler(int action)
+{
+	pr_info("hvpipe migration event %d\n", action);
+
+	/*
+	 * HVPIPE is not used (Failed to create /dev/papr-hvpipe).
+	 * So nothing to do for migration.
+	 */
+	if (!papr_hvpipe_work)
+		return;
+
+	switch (action) {
+	case HVPIPE_SUSPEND:
+		if (hvpipe_feature) {
+			/*
+			 * Disable hvpipe_feature to the user
space.
+			 * It will be enabled with RESUME event.
+			 */
+			hvpipe_feature = false;
+			/*
+			 * set system parameter hvpipe 'disable'
+			 */
+			set_hvpipe_sys_param(0);
+		}
+		break;
+	case HVPIPE_RESUME:
+		/*
+		 * set system parameter hvpipe 'enable'
+		 */
+		if (!set_hvpipe_sys_param(1))
+			hvpipe_feature = true;
+		else
+			pr_err("hvpipe is not enabled after
migration\n");

So we will end up in else condtion if destination partition does not
have hvpipe capability ?

Yes if the HVPIPE is not supported on the destination partition.

Generally we should not see this error message -  HMC is adding some
checks whether FW supports this capability and limits the migration
before upgrade the FW. But added this printk (else condition) in case.

Thanks
Haren

Thanks,
-Mahesh.

quoted

+
+		break;
+	}
+}
+
 static const struct file_operations papr_hvpipe_ops = {
 	.unlocked_ioctl	=	papr_hvpipe_dev_ioctl,
 };

@@ -731,6 +794,7 @@ static int __init papr_hvpipe_init(void)

 
 	if (!ret) {
 		pr_info("hvpipe feature is enabled\n");
+		hvpipe_feature = true;
 		return 0;
 	} else
 		pr_err("hvpipe feature is not enabled %d\n", ret);

diff --git a/arch/powerpc/platforms/pseries/papr-hvpipe.h

b/arch/powerpc/platforms/pseries/papr-hvpipe.h
index aab7f77e087d..c343f4230865 100644

--- a/arch/powerpc/platforms/pseries/papr-hvpipe.h
+++ b/arch/powerpc/platforms/pseries/papr-hvpipe.h

@@ -11,6 +11,11 @@

 
 #define	HVPIPE_HDR_LEN	sizeof(struct papr_hvpipe_hdr)
 
+enum hvpipe_migrate_action {
+	HVPIPE_SUSPEND,
+	HVPIPE_RESUME,
+};
+
 struct hvpipe_source_info {
 	struct list_head list;	/* list of sources */
 	u32 srcID;

@@ -33,4 +38,5 @@ struct hvpipe_event_buf {

 				/* with specified src ID */
 };
 
+void hvpipe_migration_handler(int action);
 #endif /* _PAPR_HVPIPE_H */
-- 
2.43.5