Subject: Re: [RESEND PATCH v7 3/5] powerpc/papr_scm: Fetch nvdimm health information from PHYP

From: Vaibhav Jain <[email-masked]>
Date: Wed, 20 May 2020 22:45:58 +0530

Thanks for reviewing this this patch Ira. My responses below:

Ira Weiny <[email-masked]> writes:

> On Wed, May 20, 2020 at 12:30:56AM +0530, Vaibhav Jain wrote:
>> Implement support for fetching nvdimm health information via
>> H_SCM_HEALTH hcall as documented in Ref[1]. The hcall returns a pair
>> of 64-bit big-endian integers, bitwise-and of which is then stored in
>> 'struct papr_scm_priv' and subsequently partially exposed to
>> user-space via newly introduced dimm specific attribute
>> 'papr/flags'. Since the hcall is costly, the health information is
>> cached and only re-queried, 60s after the previous successful hcall.
>> 
>> The patch also adds a  documentation text describing flags reported by
>> the the new sysfs attribute 'papr/flags' is also introduced at
>> Documentation/ABI/testing/sysfs-bus-papr-scm.
>> 
>> [1] commit 58b278f568f0 ("powerpc: Provide initial documentation for
>> PAPR hcalls")
>> 
>> Cc: Dan Williams <[email-masked]>
>> Cc: Michael Ellerman <[email-masked]>
>> Cc: "Aneesh Kumar K . V" <[email-masked]>
>> Signed-off-by: Vaibhav Jain <[email-masked]>
>> ---
>> Changelog:
>> 
>> Resend:
>> * None
>> 
>> v6..v7 :
>> * Used the exported buf_seq_printf() function to generate content for
>>   'papr/flags'
>> * Moved the PAPR_SCM_DIMM_* bit-flags macro definitions to papr_scm.c
>>   and removed the papr_scm.h file [Mpe]
>> * Some minor consistency issued in sysfs-bus-papr-scm
>>   documentation. [Mpe]
>> * s/dimm_mutex/health_mutex/g [Mpe]
>> * Split drc_pmem_query_health() into two function one of which takes
>>   care of caching and locking. [Mpe]
>> * Fixed a local copy creation of dimm health information using
>>   READ_ONCE(). [Mpe]
>> 
>> v5..v6 :
>> * Change the flags sysfs attribute from 'papr_flags' to 'papr/flags'
>>   [Dan Williams]
>> * Include documentation for 'papr/flags' attr [Dan Williams]
>> * Change flag 'save_fail' to 'flush_fail' [Dan Williams]
>> * Caching of health bitmap to reduce expensive hcalls [Dan Williams]
>> * Removed usage of PPC_BIT from 'papr-scm.h' header [Mpe]
>> * Replaced two __be64 integers from papr_scm_priv to a single u64
>>   integer [Mpe]
>> * Updated patch description to reflect the changes made in this
>>   version.
>> * Removed avoidable usage of 'papr_scm_priv.dimm_mutex' from
>>   flags_show() [Dan Williams]
>> 
>> v4..v5 :
>> * None
>> 
>> v3..v4 :
>> * None
>> 
>> v2..v3 :
>> * Removed PAPR_SCM_DIMM_HEALTH_NON_CRITICAL as a condition for
>>        	 NVDIMM unarmed [Aneesh]
>> 
>> v1..v2 :
>> * New patch in the series.
>> ---
>>  Documentation/ABI/testing/sysfs-bus-papr-scm |  27 +++
>>  arch/powerpc/platforms/pseries/papr_scm.c    | 169 ++++++++++++++++++-
>>  2 files changed, 194 insertions(+), 2 deletions(-)
>>  create mode 100644 Documentation/ABI/testing/sysfs-bus-papr-scm
>> 
>> diff --git a/Documentation/ABI/testing/sysfs-bus-papr-scm b/Documentation/ABI/testing/sysfs-bus-papr-scm
>> new file mode 100644
>> index 000000000000..6143d06072f1
>> --- /dev/null
>> +++ b/Documentation/ABI/testing/sysfs-bus-papr-scm
>> @@ -0,0 +1,27 @@
>> +What:		/sys/bus/nd/devices/nmemX/papr/flags
>> +Date:		Apr, 2020
>> +KernelVersion:	v5.8
>> +Contact:	linuxppc-dev <[email-masked]>, [email-masked],
>> +Description:
>> +		(RO) Report flags indicating various states of a
>> +		papr-scm NVDIMM device. Each flag maps to a one or
>> +		more bits set in the dimm-health-bitmap retrieved in
>> +		response to H_SCM_HEALTH hcall. The details of the bit
>> +		flags returned in response to this hcall is available
>> +		at 'Documentation/powerpc/papr_hcalls.rst' . Below are
>> +		the flags reported in this sysfs file:
>> +
>> +		* "not_armed"	: Indicates that NVDIMM contents will not
>> +				  survive a power cycle.
>> +		* "flush_fail"	: Indicates that NVDIMM contents
>> +				  couldn't be flushed during last
>> +				  shut-down event.
>> +		* "restore_fail": Indicates that NVDIMM contents
>> +				  couldn't be restored during NVDIMM
>> +				  initialization.
>> +		* "encrypted"	: NVDIMM contents are encrypted.
>> +		* "smart_notify": There is health event for the NVDIMM.
>> +		* "scrubbed"	: Indicating that contents of the
>> +				  NVDIMM have been scrubbed.
>> +		* "locked"	: Indicating that NVDIMM contents cant
>> +				  be modified until next power cycle.
>> diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
>> index f35592423380..142636e1a59f 100644
>> --- a/arch/powerpc/platforms/pseries/papr_scm.c
>> +++ b/arch/powerpc/platforms/pseries/papr_scm.c
>> @@ -12,6 +12,7 @@
>>  #include <linux/libnvdimm.h>
>>  #include <linux/platform_device.h>
>>  #include <linux/delay.h>
>> +#include <linux/seq_buf.h>
>>  
>>  #include <asm/plpar_wrappers.h>
>>  
>> @@ -22,6 +23,44 @@
>>  	 (1ul << ND_CMD_GET_CONFIG_DATA) | \
>>  	 (1ul << ND_CMD_SET_CONFIG_DATA))
>>  
>> +/* DIMM health bitmap bitmap indicators */
>> +/* SCM device is unable to persist memory contents */
>> +#define PAPR_SCM_DIMM_UNARMED                   (1ULL << (63 - 0))
>> +/* SCM device failed to persist memory contents */
>> +#define PAPR_SCM_DIMM_SHUTDOWN_DIRTY            (1ULL << (63 - 1))
>> +/* SCM device contents are persisted from previous IPL */
>> +#define PAPR_SCM_DIMM_SHUTDOWN_CLEAN            (1ULL << (63 - 2))
>> +/* SCM device contents are not persisted from previous IPL */
>> +#define PAPR_SCM_DIMM_EMPTY                     (1ULL << (63 - 3))
>> +/* SCM device memory life remaining is critically low */
>> +#define PAPR_SCM_DIMM_HEALTH_CRITICAL           (1ULL << (63 - 4))
>> +/* SCM device will be garded off next IPL due to failure */
>> +#define PAPR_SCM_DIMM_HEALTH_FATAL              (1ULL << (63 - 5))
>> +/* SCM contents cannot persist due to current platform health status */
>> +#define PAPR_SCM_DIMM_HEALTH_UNHEALTHY          (1ULL << (63 - 6))
>> +/* SCM device is unable to persist memory contents in certain conditions */
>> +#define PAPR_SCM_DIMM_HEALTH_NON_CRITICAL       (1ULL << (63 - 7))
>> +/* SCM device is encrypted */
>> +#define PAPR_SCM_DIMM_ENCRYPTED                 (1ULL << (63 - 8))
>> +/* SCM device has been scrubbed and locked */
>> +#define PAPR_SCM_DIMM_SCRUBBED_AND_LOCKED       (1ULL << (63 - 9))
>> +
>> +/* Bits status indicators for health bitmap indicating unarmed dimm */
>> +#define PAPR_SCM_DIMM_UNARMED_MASK (PAPR_SCM_DIMM_UNARMED |		\
>> +				    PAPR_SCM_DIMM_HEALTH_UNHEALTHY)
>> +
>> +/* Bits status indicators for health bitmap indicating unflushed dimm */
>> +#define PAPR_SCM_DIMM_BAD_SHUTDOWN_MASK (PAPR_SCM_DIMM_SHUTDOWN_DIRTY)
>> +
>> +/* Bits status indicators for health bitmap indicating unrestored dimm */
>> +#define PAPR_SCM_DIMM_BAD_RESTORE_MASK  (PAPR_SCM_DIMM_EMPTY)
>> +
>> +/* Bit status indicators for smart event notification */
>> +#define PAPR_SCM_DIMM_SMART_EVENT_MASK (PAPR_SCM_DIMM_HEALTH_CRITICAL | \
>> +					PAPR_SCM_DIMM_HEALTH_FATAL |	\
>> +					PAPR_SCM_DIMM_HEALTH_UNHEALTHY)
>> +
>> +/* private struct associated with each region */
>>  struct papr_scm_priv {
>>  	struct platform_device *pdev;
>>  	struct device_node *dn;
>> @@ -39,6 +78,15 @@ struct papr_scm_priv {
>>  	struct resource res;
>>  	struct nd_region *region;
>>  	struct nd_interleave_set nd_set;
>> +
>> +	/* Protect dimm health data from concurrent read/writes */
>> +	struct mutex health_mutex;
>> +
>> +	/* Last time the health information of the dimm was updated */
>> +	unsigned long lasthealth_jiffies;
>> +
>> +	/* Health information for the dimm */
>> +	u64 health_bitmap;
>
> I wonder if this should be typed big endian as you mention that it is in the
> commit message?
This was discussed in an earlier review of the patch series at
https://lore.kernel.org/linux-nvdimm/[email-masked]

Even though health bitmap is returned in big endian format (For ex
value 0xC00000000000000 indicates bits 0,1 set), its value is never
used. Instead only test for specific bits being set in the register is
done.

Hence using native cpu type instead of __be64 to store this value.

>
>>  };
>>  
>>  static int drc_pmem_bind(struct papr_scm_priv *p)
>> @@ -144,6 +192,62 @@ static int drc_pmem_query_n_bind(struct papr_scm_priv *p)
>>  	return drc_pmem_bind(p);
>>  }
>>  
>> +/*
>> + * Issue hcall to retrieve dimm health info and populate papr_scm_priv with the
>> + * health information.
>> + */
>> +static int __drc_pmem_query_health(struct papr_scm_priv *p)
>> +{
>> +	unsigned long ret[PLPAR_HCALL_BUFSIZE];
>
> Is this exclusive to 64bit?  Why not u64?
Yes this is specific to 64 bit as the array holds 64 bit register values
returned from PHYP. Can u64 but here that will be a departure from existing
practice within arch/powerpc code to use an unsigned long array to fetch
returned values for PHYP.

>
>> +	s64 rc;
>
> plpar_hcall() returns long and this function returns int and rc is declared
> s64?
>
> Why not have them all be long to follow plpar_hcall?
Yes 'long' type is better suited for variable 'rc' and I will get it fixed.

But the value of variable 'rc' is never directly returned from this
function, we always return kernel error codes instead. Hence the
return type of this function is consistent.

>
>> +
>> +	/* issue the hcall */
>> +	rc = plpar_hcall(H_SCM_HEALTH, ret, p->drc_index);
>> +	if (rc != H_SUCCESS) {
>> +		dev_err(&p->pdev->dev,
>> +			 "Failed to query health information, Err:%lld\n", rc);
>> +		rc = -ENXIO;
>> +		goto out;
>> +	}
>> +
>> +	p->lasthealth_jiffies = jiffies;
>> +	p->health_bitmap = 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;
>> +}
>> +
>> +/* Min interval in seconds for assuming stable dimm health */
>> +#define MIN_HEALTH_QUERY_INTERVAL 60
>> +
>> +/* Query cached health info and if needed call drc_pmem_query_health */
>> +static int drc_pmem_query_health(struct papr_scm_priv *p)
>> +{
>> +	unsigned long cache_timeout;
>> +	s64 rc;
>> +
>> +	/* Protect concurrent modifications to papr_scm_priv */
>> +	rc = mutex_lock_interruptible(&p->health_mutex);
>> +	if (rc)
>> +		return rc;
>> +
>> +	/* Jiffies offset for which the health data is assumed to be same */
>> +	cache_timeout = p->lasthealth_jiffies +
>> +		msecs_to_jiffies(MIN_HEALTH_QUERY_INTERVAL * 1000);
>> +
>> +	/* Fetch new health info is its older than MIN_HEALTH_QUERY_INTERVAL */
>> +	if (time_after(jiffies, cache_timeout))
>> +		rc = __drc_pmem_query_health(p);
>
> And back to s64 after returning int?
Agree, will change 's64 rc' to 'int rc'.

>
>> +	else
>> +		/* Assume cached health data is valid */
>> +		rc = 0;
>> +
>> +	mutex_unlock(&p->health_mutex);
>> +	return rc;
>> +}
>>  
>>  static int papr_scm_meta_get(struct papr_scm_priv *p,
>>  			     struct nd_cmd_get_config_data_hdr *hdr)
>> @@ -286,6 +390,64 @@ static int papr_scm_ndctl(struct nvdimm_bus_descriptor *nd_desc,
>>  	return 0;
>>  }
>>  
>> +static ssize_t flags_show(struct device *dev,
>> +				struct device_attribute *attr, char *buf)
>> +{
>> +	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);
>
> and back to int...
>
drc_pmem_query_health() returns an 'int' so the type of variable 'rc'
looks correct to me.

> Just make them long all through...
I think the return type for above all functions is 'int' with
an issue in drc_pmem_query_health() that you pointed out.

With that fixed the usage of 'int' return type for functions will become
consistent.

>
> Ira
>
>> +	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_SCM_DIMM_UNARMED_MASK)
>> +		seq_buf_printf(&s, "not_armed ");
>> +
>> +	if (health & PAPR_SCM_DIMM_BAD_SHUTDOWN_MASK)
>> +		seq_buf_printf(&s, "flush_fail ");
>> +
>> +	if (health & PAPR_SCM_DIMM_BAD_RESTORE_MASK)
>> +		seq_buf_printf(&s, "restore_fail ");
>> +
>> +	if (health & PAPR_SCM_DIMM_ENCRYPTED)
>> +		seq_buf_printf(&s, "encrypted ");
>> +
>> +	if (health & PAPR_SCM_DIMM_SMART_EVENT_MASK)
>> +		seq_buf_printf(&s, "smart_notify ");
>> +
>> +	if (health & PAPR_SCM_DIMM_SCRUBBED_AND_LOCKED)
>> +		seq_buf_printf(&s, "scrubbed locked ");
>> +
>> +	if (seq_buf_used(&s))
>> +		seq_buf_printf(&s, "\n");
>> +
>> +	return seq_buf_used(&s);
>> +}
>> +DEVICE_ATTR_RO(flags);
>> +
>> +/* papr_scm specific dimm attributes */
>> +static struct attribute *papr_scm_nd_attributes[] = {
>> +	&dev_attr_flags.attr,
>> +	NULL,
>> +};
>> +
>> +static struct attribute_group papr_scm_nd_attribute_group = {
>> +	.name = "papr",
>> +	.attrs = papr_scm_nd_attributes,
>> +};
>> +
>> +static const struct attribute_group *papr_scm_dimm_attr_groups[] = {
>> +	&papr_scm_nd_attribute_group,
>> +	NULL,
>> +};
>> +
>>  static int papr_scm_nvdimm_init(struct papr_scm_priv *p)
>>  {
>>  	struct device *dev = &p->pdev->dev;
>> @@ -312,8 +474,8 @@ static int papr_scm_nvdimm_init(struct papr_scm_priv *p)
>>  	dimm_flags = 0;
>>  	set_bit(NDD_LABELING, &dimm_flags);
>>  
>> -	p->nvdimm = nvdimm_create(p->bus, p, NULL, dimm_flags,
>> -				  PAPR_SCM_DIMM_CMD_MASK, 0, NULL);
>> +	p->nvdimm = nvdimm_create(p->bus, p, papr_scm_dimm_attr_groups,
>> +				  dimm_flags, PAPR_SCM_DIMM_CMD_MASK, 0, NULL);
>>  	if (!p->nvdimm) {
>>  		dev_err(dev, "Error creating DIMM object for %pOF\n", p->dn);
>>  		goto err;
>> @@ -399,6 +561,9 @@ static int papr_scm_probe(struct platform_device *pdev)
>>  	if (!p)
>>  		return -ENOMEM;
>>  
>> +	/* Initialize the dimm mutex */
>> +	mutex_init(&p->health_mutex);
>> +
>>  	/* optional DT properties */
>>  	of_property_read_u32(dn, "ibm,metadata-size", &metadata_size);
>>  
>> -- 
>> 2.26.2
>> _______________________________________________
>> Linux-nvdimm mailing list -- [email-masked]
>> To unsubscribe send an email to [email-masked]

-- 
Cheers
~ Vaibhav