Message-ID: <20200603231814.GK1505637@iweiny-DESK2.sc.intel.com>
Date:   Wed, 3 Jun 2020 16:18:15 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Vaibhav Jain <vaibhav@...ux.ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-nvdimm@...ts.01.org,
        linux-kernel@...r.kernel.org,
        Dan Williams <dan.j.williams@...el.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Oliver O'Halloran <oohall@...il.com>,
        Santosh Sivaraj <santosh@...six.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RESEND PATCH v9 5/5] powerpc/papr_scm: Implement support for
 PAPR_PDSM_HEALTH

On Thu, Jun 04, 2020 at 12:34:04AM +0530, Vaibhav Jain wrote:
> Hi Ira,
> 
> Thanks for reviewing this patch. My responses below:
> 
> Ira Weiny <ira.weiny@...el.com> writes:
> 
> > On Tue, Jun 02, 2020 at 03:44:38PM +0530, Vaibhav Jain wrote:
> >> This patch implements support for PDSM request 'PAPR_PDSM_HEALTH'
> >> that returns a newly introduced 'struct nd_papr_pdsm_health' instance
> >> containing dimm health information back to user space in response to
> >> ND_CMD_CALL. This functionality is implemented in newly introduced
> >> papr_pdsm_health() that queries the nvdimm health information and
> >> then copies this information to the package payload whose layout is
> >> defined by 'struct nd_papr_pdsm_health'.
> >> 
> >> The patch also introduces a new member 'struct papr_scm_priv.health'
> >> thats an instance of 'struct nd_papr_pdsm_health' to cache the health
> >> information of a nvdimm. As a result functions drc_pmem_query_health()
> >> and flags_show() are updated to populate and use this new struct
> >> instead of a u64 integer that was earlier used.
> >> 
> >> Cc: "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>
> >> Cc: Dan Williams <dan.j.williams@...el.com>
> >> Cc: Michael Ellerman <mpe@...erman.id.au>
> >> Cc: Ira Weiny <ira.weiny@...el.com>
> >> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
> >> Signed-off-by: Vaibhav Jain <vaibhav@...ux.ibm.com>
> >> ---
> >> Changelog:
> >> 
> >> Resend:
> >> * Added ack from Aneesh.
> >> 
> >> v8..v9:
> >> * s/PAPR_SCM_PDSM_HEALTH/PAPR_PDSM_HEALTH/g  [ Dan , Aneesh ]
> >> * s/PAPR_SCM_PSDM_DIMM_*/PAPR_PDSM_DIMM_*/g
> >> * Renamed papr_scm_get_health() to papr_psdm_health()
> >> * Updated patch description to replace papr-scm dimm with nvdimm.
> >> 
> >> v7..v8:
> >> * None
> >> 
> >> Resend:
> >> * None
> >> 
> >> v6..v7:
> >> * Updated flags_show() to use seq_buf_printf(). [Mpe]
> >> * Updated papr_scm_get_health() to use newly introduced
> >>   __drc_pmem_query_health() bypassing the cache [Mpe].
> >> 
> >> v5..v6:
> >> * Added attribute '__packed' to 'struct nd_papr_pdsm_health_v1' to
> >>   gaurd against possibility of different compilers adding different
> >>   paddings to the struct [ Dan Williams ]
> >> 
> >> * Updated 'struct nd_papr_pdsm_health_v1' to use __u8 instead of
> >>   'bool' and also updated drc_pmem_query_health() to take this into
> >>   account. [ Dan Williams ]
> >> 
> >> v4..v5:
> >> * None
> >> 
> >> v3..v4:
> >> * Call the DSM_PAPR_SCM_HEALTH service function from
> >>   papr_scm_service_dsm() instead of papr_scm_ndctl(). [Aneesh]
> >> 
> >> v2..v3:
> >> * Updated struct nd_papr_scm_dimm_health_stat_v1 to use '__xx' types
> >>   as its exported to the userspace [Aneesh]
> >> * Changed the constants DSM_PAPR_SCM_DIMM_XX indicating dimm health
> >>   from enum to #defines [Aneesh]
> >> 
> >> v1..v2:
> >> * New patch in the series
> >> ---
> >>  arch/powerpc/include/uapi/asm/papr_pdsm.h |  39 +++++++
> >>  arch/powerpc/platforms/pseries/papr_scm.c | 125 +++++++++++++++++++---
> >>  2 files changed, 147 insertions(+), 17 deletions(-)
> >> 
> >> diff --git a/arch/powerpc/include/uapi/asm/papr_pdsm.h b/arch/powerpc/include/uapi/asm/papr_pdsm.h
> >> index 6407fefcc007..411725a91591 100644
> >> --- a/arch/powerpc/include/uapi/asm/papr_pdsm.h
> >> +++ b/arch/powerpc/include/uapi/asm/papr_pdsm.h
> >> @@ -115,6 +115,7 @@ struct nd_pdsm_cmd_pkg {
> >>   */
> >>  enum papr_pdsm {
> >>  	PAPR_PDSM_MIN = 0x0,
> >> +	PAPR_PDSM_HEALTH,
> >>  	PAPR_PDSM_MAX,
> >>  };
> >>  
> >> @@ -133,4 +134,42 @@ static inline void *pdsm_cmd_to_payload(struct nd_pdsm_cmd_pkg *pcmd)
> >>  		return (void *)(pcmd->payload);
> >>  }
> >>  
> >> +/* Various nvdimm health indicators */
> >> +#define PAPR_PDSM_DIMM_HEALTHY       0
> >> +#define PAPR_PDSM_DIMM_UNHEALTHY     1
> >> +#define PAPR_PDSM_DIMM_CRITICAL      2
> >> +#define PAPR_PDSM_DIMM_FATAL         3
> >> +
> >> +/*
> >> + * Struct exchanged between kernel & ndctl in for PAPR_PDSM_HEALTH
> >> + * Various flags indicate the health status of the dimm.
> >> + *
> >> + * dimm_unarmed		: Dimm not armed. So contents wont persist.
> >> + * dimm_bad_shutdown	: Previous shutdown did not persist contents.
> >> + * dimm_bad_restore	: Contents from previous shutdown werent restored.
> >> + * dimm_scrubbed	: Contents of the dimm have been scrubbed.
> >> + * dimm_locked		: Contents of the dimm cant be modified until CEC reboot
> >> + * dimm_encrypted	: Contents of dimm are encrypted.
> >> + * dimm_health		: Dimm health indicator. One of PAPR_PDSM_DIMM_XXXX
> >> + */
> >> +struct nd_papr_pdsm_health_v1 {
> >> +	__u8 dimm_unarmed;
> >> +	__u8 dimm_bad_shutdown;
> >> +	__u8 dimm_bad_restore;
> >> +	__u8 dimm_scrubbed;
> >> +	__u8 dimm_locked;
> >> +	__u8 dimm_encrypted;
> >> +	__u16 dimm_health;
> >> +} __packed;
> >> +
> >> +/*
> >> + * Typedef the current struct for dimm_health so that any application
> >> + * or kernel recompiled after introducing a new version automatically
> >> + * supports the new version.
> >> + */
> >> +#define nd_papr_pdsm_health nd_papr_pdsm_health_v1
> >> +
> >> +/* Current version number for the dimm health struct */
> >
> > This can't be the 'current' version.  You will need a list of versions you
> > support.  Because if the user passes in an old version you need to be able to
> > respond with that old version.  Also if you plan to support 'return X for a Y
> > query' then the user will need both X and Y defined to interpret X.
> Yes, and that change will be introduced with addition of version-2 of
> nd_papr_pdsm_health. Earlier version of the patchset[1] had such a table
> implemented. But to simplify the patchset, as we are only dealing with
> version-1 of the structs right now, it was dropped.
> 
> [1] :
> https://lore.kernel.org/linuxppc-dev/20200220095805.197229-9-vaibhav@linux.ibm.com/

I'm not sure I follow that comment.

I feel like there is some confusion about what firmware can return vs the UAPI
structure.  You have already marshaled the data between the 2.  We can define
whatever we want for the UAPI structures throwing away data the kernel does not
understand from the firmware.

> 
> >
> >> +#define ND_PAPR_PDSM_HEALTH_VERSION 1
> >> +
> >>  #endif /* _UAPI_ASM_POWERPC_PAPR_PDSM_H_ */
> >> diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
> >> index 5e2237e7ec08..c0606c0c659c 100644
> >> --- a/arch/powerpc/platforms/pseries/papr_scm.c
> >> +++ b/arch/powerpc/platforms/pseries/papr_scm.c
> >> @@ -88,7 +88,7 @@ struct papr_scm_priv {
> >>  	unsigned long lasthealth_jiffies;
> >>  
> >>  	/* Health information for the dimm */
> >> -	u64 health_bitmap;
> >> +	struct nd_papr_pdsm_health health;
> >
> > ok so we are throwing away all the #defs from patch 1?  Are they still valid?
> >
> > I'm confused that patch 3 added this and we are throwing it away
> > here...
> The #defines are still valid, only the usage moved to a __drc_pmem_query_health().
> 
> >
> >>  };
> >>  
> >>  static int drc_pmem_bind(struct papr_scm_priv *p)
> >> @@ -201,6 +201,7 @@ static int drc_pmem_query_n_bind(struct papr_scm_priv *p)
> >>  static int __drc_pmem_query_health(struct papr_scm_priv *p)
> >>  {
> >>  	unsigned long ret[PLPAR_HCALL_BUFSIZE];
> >> +	u64 health;
> >>  	long rc;
> >>  
> >>  	/* issue the hcall */
> >> @@ -208,18 +209,46 @@ static int __drc_pmem_query_health(struct papr_scm_priv *p)
> >>  	if (rc != H_SUCCESS) {
> >>  		dev_err(&p->pdev->dev,
> >>  			 "Failed to query health information, Err:%ld\n", rc);
> >> -		rc = -ENXIO;
> >> -		goto out;
> >> +		return -ENXIO;
> >
> > I missed this...  probably did not need the goto in the first patch?
> Yes, will get rid of the goto from patch-1.

Cool.

> 
> >
> >>  	}
> >>  
> >>  	p->lasthealth_jiffies = jiffies;
> >> -	p->health_bitmap = ret[0] & ret[1];
> >> +	health = ret[0] & ret[1];
> >>  
> >>  	dev_dbg(&p->pdev->dev,
> >>  		"Queried dimm health info. Bitmap:0x%016lx Mask:0x%016lx\n",
> >>  		ret[0], ret[1]);
> >> -out:
> >> -	return rc;
> >> +
> >> +	memset(&p->health, 0, sizeof(p->health));
> >> +
> >> +	/* Check for various masks in bitmap and set the buffer */
> >> +	if (health & PAPR_PMEM_UNARMED_MASK)
> >
> > Oh ok...  odd.  (don't add code then just take it away in a series)
> > You could have lead with the user structure and put this code in patch
> > 3.
> The struct nd_papr_pdsm_health in only introduced this patch in header
> 'papr_pdsm.h' as means of exchanging nvdimm health information with
> userspace. Introducing this struct without introducing the necessary
> scafolding in 'papr_pdsm.h' would have been very counter-intutive.

I respectfully disagree.  You intended to use a copy of this structure in
kernel to store the data.  Just do that.

> 
> >
> > Why does the user need u8 to represent a single bit?  Does this help protect
> > against endian issues?
> This was 'bool' earlier but since type 'bool' isnt suitable for ioctl abi
> and I wanted to avoid bit fields here as not sure if their packing may
> differ across compilers hence replaced with u8.
> 

ok works for me...

> >
> >> +		p->health.dimm_unarmed = 1;
> >> +
> >> +	if (health & PAPR_PMEM_BAD_SHUTDOWN_MASK)
> >> +		p->health.dimm_bad_shutdown = 1;
> >> +
> >> +	if (health & PAPR_PMEM_BAD_RESTORE_MASK)
> >> +		p->health.dimm_bad_restore = 1;
> >> +
> >> +	if (health & PAPR_PMEM_ENCRYPTED)
> >> +		p->health.dimm_encrypted = 1;
> >> +
> >> +	if (health & PAPR_PMEM_SCRUBBED_AND_LOCKED) {
> >> +		p->health.dimm_locked = 1;
> >> +		p->health.dimm_scrubbed = 1;
> >> +	}
> >> +
> >> +	if (health & PAPR_PMEM_HEALTH_UNHEALTHY)
> >> +		p->health.dimm_health = PAPR_PDSM_DIMM_UNHEALTHY;
> >> +
> >> +	if (health & PAPR_PMEM_HEALTH_CRITICAL)
> >> +		p->health.dimm_health = PAPR_PDSM_DIMM_CRITICAL;
> >> +
> >> +	if (health & PAPR_PMEM_HEALTH_FATAL)
> >> +		p->health.dimm_health = PAPR_PDSM_DIMM_FATAL;
> >> +
> >> +	return 0;
> >>  }
> >>  
> >>  /* Min interval in seconds for assuming stable dimm health */
> >> @@ -403,6 +432,58 @@ static int is_cmd_valid(struct nvdimm *nvdimm, unsigned int cmd, void *buf,
> >>  	return 0;
> >>  }
> >>  
> >> +/* Fetch the DIMM health info and populate it in provided package. */
> >> +static int papr_pdsm_health(struct papr_scm_priv *p,
> >> +			       struct nd_pdsm_cmd_pkg *pkg)
> >> +{
> >> +	int rc;
> >> +	size_t copysize = sizeof(p->health);
> >> +
> >> +	/* Ensure dimm health mutex is taken preventing concurrent access */
> >> +	rc = mutex_lock_interruptible(&p->health_mutex);
> >> +	if (rc)
> >> +		goto out;
> >> +
> >> +	/* Always fetch upto date dimm health data ignoring cached values */
> >> +	rc = __drc_pmem_query_health(p);
> >> +	if (rc)
> >> +		goto out_unlock;
> >> +	/*
> >> +	 * If the requested payload version is greater than one we know
> >> +	 * about, return the payload version we know about and let
> >> +	 * caller/userspace handle.
> >> +	 */
> >> +	if (pkg->payload_version > ND_PAPR_PDSM_HEALTH_VERSION)
> >> +		pkg->payload_version = ND_PAPR_PDSM_HEALTH_VERSION;
> >
> > I know this seems easy now but I do think you will run into trouble later.
> 
> I did addressed this in an earlier iteration of this patchset[1] and
> dropped it in favour of simplicity.
> 
> [1] :
> https://lore.kernel.org/linuxppc-dev/20200220095805.197229-9-vaibhav@linux.ibm.com/
 
I don't see how that addresses this?  See my other email.

Ira

> 
> > Ira
> >
> >> +
> >> +	if (pkg->hdr.nd_size_out < copysize) {
> >> +		dev_dbg(&p->pdev->dev, "Truncated payload (%u). Expected (%lu)",
> >> +			pkg->hdr.nd_size_out, copysize);
> >> +		rc = -ENOSPC;
> >> +		goto out_unlock;
> >> +	}
> >> +
> >> +	dev_dbg(&p->pdev->dev, "Copying payload size=%lu version=0x%x\n",
> >> +		copysize, pkg->payload_version);
> >> +
> >> +	/* Copy the health struct to the payload */
> >> +	memcpy(pdsm_cmd_to_payload(pkg), &p->health, copysize);
> >> +	pkg->hdr.nd_fw_size = copysize;
> >> +
> >> +out_unlock:
> >> +	mutex_unlock(&p->health_mutex);
> >> +
> >> +out:
> >> +	/*
> >> +	 * Put the error in out package and return success from function
> >> +	 * so that errors if any are propogated back to userspace.
> >> +	 */
> >> +	pkg->cmd_status = rc;
> >> +	dev_dbg(&p->pdev->dev, "completion code = %d\n", rc);
> >> +
> >> +	return 0;
> >> +}
> >> +
> >>  static int papr_scm_service_pdsm(struct papr_scm_priv *p,
> >>  				struct nd_pdsm_cmd_pkg *call_pkg)
> >>  {
> >> @@ -417,6 +498,9 @@ static int papr_scm_service_pdsm(struct papr_scm_priv *p,
> >>  
> >>  	/* Depending on the DSM command call appropriate service routine */
> >>  	switch (call_pkg->hdr.nd_command) {
> >> +	case PAPR_PDSM_HEALTH:
> >> +		return papr_pdsm_health(p, call_pkg);
> >> +
> >>  	default:
> >>  		dev_dbg(&p->pdev->dev, "Unsupported PDSM request 0x%llx\n",
> >>  			call_pkg->hdr.nd_command);
> >> @@ -485,34 +569,41 @@ static ssize_t flags_show(struct device *dev,
> >>  	struct nvdimm *dimm = to_nvdimm(dev);
> >>  	struct papr_scm_priv *p = nvdimm_provider_data(dimm);
> >>  	struct seq_buf s;
> >> -	u64 health;
> >>  	int rc;
> >>  
> >>  	rc = drc_pmem_query_health(p);
> >>  	if (rc)
> >>  		return rc;
> >>  
> >> -	/* Copy health_bitmap locally, check masks & update out buffer */
> >> -	health = READ_ONCE(p->health_bitmap);
> >> -
> >>  	seq_buf_init(&s, buf, PAGE_SIZE);
> >> -	if (health & PAPR_PMEM_UNARMED_MASK)
> >> +
> >> +	/* Protect concurrent modifications to papr_scm_priv */
> >> +	rc = mutex_lock_interruptible(&p->health_mutex);
> >> +	if (rc)
> >> +		return rc;
> >> +
> >> +	if (p->health.dimm_unarmed)
> >>  		seq_buf_printf(&s, "not_armed ");
> >>  
> >> -	if (health & PAPR_PMEM_BAD_SHUTDOWN_MASK)
> >> +	if (p->health.dimm_bad_shutdown)
> >>  		seq_buf_printf(&s, "flush_fail ");
> >>  
> >> -	if (health & PAPR_PMEM_BAD_RESTORE_MASK)
> >> +	if (p->health.dimm_bad_restore)
> >>  		seq_buf_printf(&s, "restore_fail ");
> >>  
> >> -	if (health & PAPR_PMEM_ENCRYPTED)
> >> +	if (p->health.dimm_encrypted)
> >>  		seq_buf_printf(&s, "encrypted ");
> >>  
> >> -	if (health & PAPR_PMEM_SMART_EVENT_MASK)
> >> +	if (p->health.dimm_health)
> >>  		seq_buf_printf(&s, "smart_notify ");
> >>  
> >> -	if (health & PAPR_PMEM_SCRUBBED_AND_LOCKED)
> >> -		seq_buf_printf(&s, "scrubbed locked ");
> >> +	if (p->health.dimm_scrubbed)
> >> +		seq_buf_printf(&s, "scrubbed ");
> >> +
> >> +	if (p->health.dimm_locked)
> >> +		seq_buf_printf(&s, "locked ");
> >> +
> >> +	mutex_unlock(&p->health_mutex);
> >>  
> >>  	if (seq_buf_used(&s))
> >>  		seq_buf_printf(&s, "\n");
> >> -- 
> >> 2.26.2
> >> 
> 
> -- 
> Cheers
> ~ Vaibhav

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