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Date:   Wed, 3 Jun 2020 16:22:45 -0700
From:   Ira Weiny <ira.weiny@intel.com>
To:     Vaibhav Jain <vaibhav@linux.ibm.com>
Cc:     linux-nvdimm@lists.01.org, linux-kernel@vger.kernel.org,
        Steven Rostedt <rostedt@goodmis.org>,
        "Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>,
        linuxppc-dev@lists.ozlabs.org
Subject: Re: [RESEND PATCH v9 4/5] ndctl/papr_scm,uapi: Add support for PAPR
 nvdimm specific methods
Message-ID: <20200603232244.GL1505637@iweiny-DESK2.sc.intel.com>
References: <20200602101438.73929-1-vaibhav@linux.ibm.com>
 <20200602101438.73929-5-vaibhav@linux.ibm.com>
 <20200602205148.GF1505637@iweiny-DESK2.sc.intel.com>
 <20200602210553.GG1505637@iweiny-DESK2.sc.intel.com>
 <87lfl3hp2n.fsf@linux.ibm.com>
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On Thu, Jun 04, 2020 at 01:58:00AM +0530, Vaibhav Jain wrote:
> Hi Ira,
> 
> Thanks again for reviewing this patch. My Response below:
> 
> Ira Weiny <ira.weiny@intel.com> writes:
> 
> > On Tue, Jun 02, 2020 at 01:51:49PM -0700, 'Ira Weiny' wrote:
> >> On Tue, Jun 02, 2020 at 03:44:37PM +0530, Vaibhav Jain wrote:
> >
> > ...
> >
> >> > +
> >> > +/*
> >> > + * PDSM Envelope:
> >> > + *
> >> > + * The ioctl ND_CMD_CALL transfers data between user-space and kernel via
> >> > + * envelope which consists of a header and user-defined payload sections.
> >> > + * The header is described by 'struct nd_pdsm_cmd_pkg' which expects a
> >> > + * payload following it and accessible via 'nd_pdsm_cmd_pkg.payload' field.
> >> > + * There is reserved field that can used to introduce new fields to the
> >> > + * structure in future. It also tries to ensure that 'nd_pdsm_cmd_pkg.payload'
> >> > + * lies at a 8-byte boundary.
> >> > + *
> >> > + *  +-------------+---------------------+---------------------------+
> >> > + *  |   64-Bytes  |       16-Bytes      |       Max 176-Bytes       |
> >> > + *  +-------------+---------------------+---------------------------+
> >> > + *  |               nd_pdsm_cmd_pkg     |                           |
> >> > + *  |-------------+                     |                           |
> >> > + *  |  nd_cmd_pkg |                     |                           |
> >> > + *  +-------------+---------------------+---------------------------+
> >> > + *  | nd_family   |                     |                           |
> >> > + *  | nd_size_out | cmd_status          |                           |
> >> > + *  | nd_size_in  | payload_version     |     payload               |
> >> > + *  | nd_command  | reserved            |                           |
> >> > + *  | nd_fw_size  |                     |                           |
> >> > + *  +-------------+---------------------+---------------------------+
> >
> > One more comment WRT nd_size_[in|out].  I know that it is defined as the size
> > of the FW payload but normally when you nest headers 'size' in Header A
> > represents everything after Header A, including Header B.  In this case that
> > would be including nd_pdsm_cmd_pkg...
> >
> > It looks like that is not what you have done?  Or perhaps I missed it?
> >
> Not sure if I understand the question correctly.
> 'struct nd_pdsm_cmd_pkg' contains 'struct nd_cmd_pkg' at its head and
> its size_[in|out] are populated by the libndctl in userspace, setting
> them to data following the 'struct nd_cmd_pkg'.
> 
> Copying of 'struct nd_cmd_pkg' to the input/out envelop is implicitly
> done in __nd_ioctl via the command descriptor array
> __nd_cmd_bus_descs. So I dont need to add the size of 'struct
> nd_cmd_pkg' to nd_size_[in|out].

Yea I see that now...  Coming from a networking background I find that odd...
:-/  Usually 'size' in a header includes all data after that header.  Because
header A knows nothing of the rest of the 'payload'...

FWIW you could define nd_size_in anyway you want because you are not really
sending any payload back from firmware directly.  But I suppose I can live with
it.

Ira

> 
> > Ira
> >
> >> > + *
> >> > + * PDSM Header:
> >> > + *
> >> > + * The header is defined as 'struct nd_pdsm_cmd_pkg' which embeds a
> >> > + * 'struct nd_cmd_pkg' instance. The PDSM command is assigned to member
> >> > + * 'nd_cmd_pkg.nd_command'. Apart from size information of the envelope which is
> >> > + * contained in 'struct nd_cmd_pkg', the header also has members following 
> >>                                                              ^^^^^
> >>                                                         ...  the  ...
> >> 
> >> > + * members:
> >> > + *
> >> > + * 'cmd_status'		: (Out) Errors if any encountered while servicing PDSM.
> >> > + * 'payload_version'	: (In/Out) Version number associated with the payload.
> >> > + * 'reserved'		: Not used and reserved for future.
> >> > + *
> >> > + * PDSM Payload:
> >> > + *
> >> > + * The layout of the PDSM Payload is defined by various structs shared between
> >> > + * papr_scm and libndctl so that contents of payload can be interpreted. During
> >> > + * servicing of a PDSM the papr_scm module will read input args from the payload
> >> > + * field by casting its contents to an appropriate struct pointer based on the
> >> > + * PDSM command. Similarly the output of servicing the PDSM command will be
> >> > + * copied to the payload field using the same struct.
> >> > + *
> >> > + * 'libnvdimm' enforces a hard limit of 256 bytes on the envelope size, which
> >> > + * leaves around 176 bytes for the envelope payload (ignoring any padding that
> >> > + * the compiler may silently introduce).
> >> > + *
> >> > + * Payload Version:
> >> > + *
> >> > + * A 'payload_version' field is present in PDSM header that indicates a specific
> >> > + * version of the structure present in PDSM Payload for a given PDSM command.
> >> > + * This provides backward compatibility in case the PDSM Payload structure
> >> > + * evolves and different structures are supported by 'papr_scm' and 'libndctl'.
> >> > + *
> >> > + * When sending a PDSM Payload to 'papr_scm', 'libndctl' should send the version
> >> > + * of the payload struct it supports via 'payload_version' field. The 'papr_scm'
> >> > + * module when servicing the PDSM envelope checks the 'payload_version' and then
> >> > + * uses 'payload struct version' == MIN('payload_version field',
> >> > + * 'max payload-struct-version supported by papr_scm') to service the PDSM.
> >> > + * After servicing the PDSM, 'papr_scm' put the negotiated version of payload
> >> > + * struct in returned 'payload_version' field.
> >> > + *
> >> > + * Libndctl on receiving the envelope back from papr_scm again checks the
> >> > + * 'payload_version' field and based on it use the appropriate version dsm
> >> > + * struct to parse the results.
> >> > + *
> >> > + * Backward Compatibility:
> >> > + *
> >> > + * Above scheme of exchanging different versioned PDSM struct between libndctl
> >> > + * and papr_scm should provide backward compatibility until following two
> >> > + * assumptions/conditions when defining new PDSM structs hold:
> >> > + *
> >> > + * Let T(X) = { set of attributes in PDSM struct 'T' versioned X }
> >> > + *
> >> > + * 1. T(X) is a proper subset of T(Y) if Y > X.
> >> > + *    i.e Each new version of PDSM struct should retain existing struct
> >> > + *    attributes from previous version
> >> > + *
> >> > + * 2. If an entity (libndctl or papr_scm) supports a PDSM struct T(X) then
> >> > + *    it should also support T(1), T(2)...T(X - 1).
> >> > + *    i.e When adding support for new version of a PDSM struct, libndctl
> >> > + *    and papr_scm should retain support of the existing PDSM struct
> >> > + *    version they support.
> >> 
> >> Please see this thread for an example why versions are a bad idea in UAPIs:
> >> 
> >> https://lkml.org/lkml/2020/3/26/213
> >> 
> >> While the use of version is different in that thread the fundamental issues are
> >> the same.  You end up with some weird matrix of supported features and
> >> structure definitions.  For example, you are opening up the possibility of
> >> changing structures with a different version for no good reason.
> >> 
> >> Also having the user query with version Z and get back version X (older) is
> >> odd.  Generally if the kernel does not know about a feature (ie version Z of
> >> the structure) it should return -EINVAL and let the user figure out what to do.
> >> The user may just give up or they could try a different query.
> >> 
> >> > + */
> >> > +
> >> > +/* PDSM-header + payload expected with ND_CMD_CALL ioctl from libnvdimm */
> >> > +struct nd_pdsm_cmd_pkg {
> >> > +	struct nd_cmd_pkg hdr;	/* Package header containing sub-cmd */
> >> > +	__s32 cmd_status;	/* Out: Sub-cmd status returned back */
> >> > +	__u16 reserved[5];	/* Ignored and to be used in future */
> >> 
> >> How do you know when reserved is used for something else in the future?  Is
> >> reserved guaranteed (and checked by the code) to be 0?
> >> 
> >> > +	__u16 payload_version;	/* In/Out: version of the payload */
> >> 
> >> Why is payload_version after reserved?
> >> 
> >> > +	__u8 payload[];		/* In/Out: Sub-cmd data buffer */
> >> > +} __packed;
> >> > +
> >> > +/*
> >> > + * Methods to be embedded in ND_CMD_CALL request. These are sent to the kernel
> >> > + * via 'nd_pdsm_cmd_pkg.hdr.nd_command' member of the ioctl struct
> >> > + */
> >> > +enum papr_pdsm {
> >> > +	PAPR_PDSM_MIN = 0x0,
> >> > +	PAPR_PDSM_MAX,
> >> > +};
> >> > +
> >> > +/* Convert a libnvdimm nd_cmd_pkg to pdsm specific pkg */
> >> > +static inline struct nd_pdsm_cmd_pkg *nd_to_pdsm_cmd_pkg(struct nd_cmd_pkg *cmd)
> >> > +{
> >> > +	return (struct nd_pdsm_cmd_pkg *) cmd;
> >> > +}
> >> > +
> >> > +/* Return the payload pointer for a given pcmd */
> >> > +static inline void *pdsm_cmd_to_payload(struct nd_pdsm_cmd_pkg *pcmd)
> >> > +{
> >> > +	if (pcmd->hdr.nd_size_in == 0 && pcmd->hdr.nd_size_out == 0)
> >> > +		return NULL;
> >> > +	else
> >> > +		return (void *)(pcmd->payload);
> >> > +}
> >> > +
> >> > +#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 149431594839..5e2237e7ec08 100644
> >> > --- a/arch/powerpc/platforms/pseries/papr_scm.c
> >> > +++ b/arch/powerpc/platforms/pseries/papr_scm.c
> >> > @@ -15,13 +15,15 @@
> >> >  #include <linux/seq_buf.h>
> >> >  
> >> >  #include <asm/plpar_wrappers.h>
> >> > +#include <asm/papr_pdsm.h>
> >> >  
> >> >  #define BIND_ANY_ADDR (~0ul)
> >> >  
> >> >  #define PAPR_SCM_DIMM_CMD_MASK \
> >> >  	((1ul << ND_CMD_GET_CONFIG_SIZE) | \
> >> >  	 (1ul << ND_CMD_GET_CONFIG_DATA) | \
> >> > -	 (1ul << ND_CMD_SET_CONFIG_DATA))
> >> > +	 (1ul << ND_CMD_SET_CONFIG_DATA) | \
> >> > +	 (1ul << ND_CMD_CALL))
> >> >  
> >> >  /* DIMM health bitmap bitmap indicators */
> >> >  /* SCM device is unable to persist memory contents */
> >> > @@ -350,16 +352,97 @@ static int papr_scm_meta_set(struct papr_scm_priv *p,
> >> >  	return 0;
> >> >  }
> >> >  
> >> > +/*
> >> > + * Validate the inputs args to dimm-control function and return '0' if valid.
> >> > + * This also does initial sanity validation to ND_CMD_CALL sub-command packages.
> >> > + */
> >> > +static int is_cmd_valid(struct nvdimm *nvdimm, unsigned int cmd, void *buf,
> >> > +		       unsigned int buf_len)
> >> > +{
> >> > +	unsigned long cmd_mask = PAPR_SCM_DIMM_CMD_MASK;
> >> > +	struct nd_pdsm_cmd_pkg *pkg = nd_to_pdsm_cmd_pkg(buf);
> >> > +	struct papr_scm_priv *p;
> >> > +
> >> > +	/* Only dimm-specific calls are supported atm */
> >> > +	if (!nvdimm)
> >> > +		return -EINVAL;
> >> > +
> >> > +	/* get the provider date from struct nvdimm */
> >> 
> >> s/date/data
> >> 
> >> > +	p = nvdimm_provider_data(nvdimm);
> >> > +
> >> > +	if (!test_bit(cmd, &cmd_mask)) {
> >> > +		dev_dbg(&p->pdev->dev, "Unsupported cmd=%u\n", cmd);
> >> > +		return -EINVAL;
> >> > +	} else if (cmd == ND_CMD_CALL) {
> >> > +
> >> > +		/* Verify the envelope package */
> >> > +		if (!buf || buf_len < sizeof(struct nd_pdsm_cmd_pkg)) {
> >> > +			dev_dbg(&p->pdev->dev, "Invalid pkg size=%u\n",
> >> > +				buf_len);
> >> > +			return -EINVAL;
> >> > +		}
> >> > +
> >> > +		/* Verify that the PDSM family is valid */
> >> > +		if (pkg->hdr.nd_family != NVDIMM_FAMILY_PAPR) {
> >> > +			dev_dbg(&p->pdev->dev, "Invalid pkg family=0x%llx\n",
> >> > +				pkg->hdr.nd_family);
> >> > +			return -EINVAL;
> >> > +
> >> > +		}
> >> > +
> >> > +		/* We except a payload with all PDSM commands */
> >> > +		if (pdsm_cmd_to_payload(pkg) == NULL) {
> >> > +			dev_dbg(&p->pdev->dev,
> >> > +				"Empty payload for sub-command=0x%llx\n",
> >> > +				pkg->hdr.nd_command);
> >> > +			return -EINVAL;
> >> > +		}
> >> > +	}
> >> > +
> >> > +	/* Command looks valid */
> >> 
> >> I assume the first command to be implemented also checks the { nd_command,
> >> payload_version, payload length } for correctness?
> >> 
> >> > +	return 0;
> >> > +}
> >> > +
> >> > +static int papr_scm_service_pdsm(struct papr_scm_priv *p,
> >> > +				struct nd_pdsm_cmd_pkg *call_pkg)
> >> > +{
> >> > +	/* unknown subcommands return error in packages */
> >> > +	if (call_pkg->hdr.nd_command <= PAPR_PDSM_MIN ||
> >> > +	    call_pkg->hdr.nd_command >= PAPR_PDSM_MAX) {
> >> > +		dev_dbg(&p->pdev->dev, "Invalid PDSM request 0x%llx\n",
> >> > +			call_pkg->hdr.nd_command);
> >> > +		call_pkg->cmd_status = -EINVAL;
> >> > +		return 0;
> >> > +	}
> >> > +
> >> > +	/* Depending on the DSM command call appropriate service routine */
> >> > +	switch (call_pkg->hdr.nd_command) {
> >> > +	default:
> >> > +		dev_dbg(&p->pdev->dev, "Unsupported PDSM request 0x%llx\n",
> >> > +			call_pkg->hdr.nd_command);
> >> > +		call_pkg->cmd_status = -ENOENT;
> >> > +		return 0;
> >> > +	}
> >> > +}
> >> > +
> >> >  static int papr_scm_ndctl(struct nvdimm_bus_descriptor *nd_desc,
> >> >  			  struct nvdimm *nvdimm, unsigned int cmd, void *buf,
> >> >  			  unsigned int buf_len, int *cmd_rc)
> >> >  {
> >> >  	struct nd_cmd_get_config_size *get_size_hdr;
> >> >  	struct papr_scm_priv *p;
> >> > +	struct nd_pdsm_cmd_pkg *call_pkg = NULL;
> >> > +	int rc;
> >> >  
> >> > -	/* Only dimm-specific calls are supported atm */
> >> > -	if (!nvdimm)
> >> > -		return -EINVAL;
> >> > +	/* Use a local variable in case cmd_rc pointer is NULL */
> >> > +	if (cmd_rc == NULL)
> >> > +		cmd_rc = &rc;
> >> 
> >> Why is this needed?  AFAICT The caller of papr_scm_ndctl does not specify null
> >> and you did not change it.
> >> 
> >> > +
> >> > +	*cmd_rc = is_cmd_valid(nvdimm, cmd, buf, buf_len);
> >> > +	if (*cmd_rc) {
> >> > +		pr_debug("Invalid cmd=0x%x. Err=%d\n", cmd, *cmd_rc);
> >> > +		return *cmd_rc;
> >> > +	}
> >> >  
> >> >  	p = nvdimm_provider_data(nvdimm);
> >> >  
> >> > @@ -381,13 +464,19 @@ static int papr_scm_ndctl(struct nvdimm_bus_descriptor *nd_desc,
> >> >  		*cmd_rc = papr_scm_meta_set(p, buf);
> >> >  		break;
> >> >  
> >> > +	case ND_CMD_CALL:
> >> > +		call_pkg = nd_to_pdsm_cmd_pkg(buf);
> >> > +		*cmd_rc = papr_scm_service_pdsm(p, call_pkg);
> >> > +		break;
> >> > +
> >> >  	default:
> >> > -		return -EINVAL;
> >> > +		dev_dbg(&p->pdev->dev, "Unknown command = %d\n", cmd);
> >> > +		*cmd_rc = -EINVAL;
> >> 
> >> Is this change related?  If there is a bug where there is a caller of
> >> papr_scm_ndctl() with cmd_rc == NULL this should be a separate patch to fix
> >> that issue.
> >> 
> >> Ira
> >> 
> >> >  	}
> >> >  
> >> >  	dev_dbg(&p->pdev->dev, "returned with cmd_rc = %d\n", *cmd_rc);
> >> >  
> >> > -	return 0;
> >> > +	return *cmd_rc;
> >> >  }
> >> >  
> >> >  static ssize_t flags_show(struct device *dev,
> >> > diff --git a/include/uapi/linux/ndctl.h b/include/uapi/linux/ndctl.h
> >> > index de5d90212409..0e09dc5cec19 100644
> >> > --- a/include/uapi/linux/ndctl.h
> >> > +++ b/include/uapi/linux/ndctl.h
> >> > @@ -244,6 +244,7 @@ struct nd_cmd_pkg {
> >> >  #define NVDIMM_FAMILY_HPE2 2
> >> >  #define NVDIMM_FAMILY_MSFT 3
> >> >  #define NVDIMM_FAMILY_HYPERV 4
> >> > +#define NVDIMM_FAMILY_PAPR 5
> >> >  
> >> >  #define ND_IOCTL_CALL			_IOWR(ND_IOCTL, ND_CMD_CALL,\
> >> >  					struct nd_cmd_pkg)
> >> > -- 
> >> > 2.26.2
> >> > 
> >> _______________________________________________
> >> Linux-nvdimm mailing list -- linux-nvdimm@lists.01.org
> >> To unsubscribe send an email to linux-nvdimm-leave@lists.01.org
> 
> -- 
> Cheers
> ~ Vaibhav