Re: [PATCH v2 9/9] powerpc/pseries: HVPIPE changes to support migration

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

On Mon, 2025-08-25 at 14:10 +0530, Mahesh J Salgaonkar wrote:
> On 2025-08-12 15:57:13 Tue, Haren Myneni wrote:
> > 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.
> 
> > +
> > +		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
> > 
> >