Re: [RESEND PATCH v7 4/5] ndctl/papr_scm,uapi: Add support for PAPR nvdimm specific methods

Vaibhav Jain
2020-05-20T18:47:50Z

Thanks for reviewing this patch Ira. My responses below:

Ira Weiny <ira.weiny@intel.com> writes:

> On Wed, May 20, 2020 at 12:30:57AM +0530, Vaibhav Jain wrote:
>> Introduce support for Papr nvDimm Specific Methods (PDSM) in papr_scm
>> modules and add the command family to the white list of NVDIMM command
>> sets. Also advertise support for ND_CMD_CALL for the dimm
>> command mask and implement necessary scaffolding in the module to
>> handle ND_CMD_CALL ioctl and PDSM requests that we receive.
>>
>> The layout of the PDSM request as we expect from libnvdimm/libndctl is
>> described in newly introduced uapi header 'papr_scm_pdsm.h' which
>> defines a new 'struct nd_pdsm_cmd_pkg' header. This header is used
>> to communicate the PDSM request via member
>> 'nd_pkg_papr_scm->nd_command' and size of payload that need to be
>> sent/received for servicing the PDSM.
>>
>> A new function is_cmd_valid() is implemented that reads the args to
>> papr_scm_ndctl() and performs sanity tests on them. A new function
>> papr_scm_service_pdsm() is introduced and is called from
>> papr_scm_ndctl() in case of a PDSM request is received via ND_CMD_CALL
>> command from libnvdimm.
>>
>> Cc: Dan Williams <dan.j.williams@intel.com>
>> Cc: Michael Ellerman <mpe@ellerman.id.au>
>> Cc: "Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>
>> Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>
>> ---
>> Changelog:
>>
>> Resend:
>> * None
>>
>> v6..v7 :
>> * Removed the re-definitions of __packed macro from papr_scm_pdsm.h
>> [Mpe].
>> * Removed the usage of __KERNEL__ macros in papr_scm_pdsm.h [Mpe].
>> * Removed macros that were unused in papr_scm.c from papr_scm_pdsm.h
>> [Mpe].
>> * Made functions defined in papr_scm_pdsm.h as static inline. [Mpe]
>>
>> v5..v6 :
>> * Changed the usage of the term DSM to PDSM to distinguish it from the
>> ACPI term [ Dan Williams ]
>> * Renamed papr_scm_dsm.h to papr_scm_pdsm.h and updated various struct
>> to reflect the new terminology.
>> * Updated the patch description and title to reflect the new terminology.
>> * Squashed patch to introduce new command family in 'ndctl.h' with
>> this patch [ Dan Williams ]
>> * Updated the papr_scm_pdsm method starting index from 0x10000 to 0x0
>> [ Dan Williams ]
>> * Removed redundant license text from the papr_scm_psdm.h file.
>> [ Dan Williams ]
>> * s/envelop/envelope/ at various places [ Dan Williams ]
>> * Added '__packed' attribute to command package header to gaurd
>> against different compiler adding paddings between the fields.
>> [ Dan Williams]
>> * Converted various pr_debug to dev_debug [ Dan Williams ]
>>
>> v4..v5 :
>> * None
>>
>> v3..v4 :
>> * None
>>
>> v2..v3 :
>> * Updated the patch prefix to 'ndctl/uapi' [Aneesh]
>>
>> v1..v2 :
>> * None
>> ---
>> arch/powerpc/include/uapi/asm/papr_scm_pdsm.h | 134 ++++++++++++++++++
>> arch/powerpc/platforms/pseries/papr_scm.c | 101 ++++++++++++-
>> include/uapi/linux/ndctl.h | 1 +
>> 3 files changed, 230 insertions(+), 6 deletions(-)
>> create mode 100644 arch/powerpc/include/uapi/asm/papr_scm_pdsm.h
>>
>> diff --git a/arch/powerpc/include/uapi/asm/papr_scm_pdsm.h b/arch/powerpc/include/uapi/asm/papr_scm_pdsm.h
>> new file mode 100644
>> index 000000000000..671693439c1c
>> --- /dev/null
>> +++ b/arch/powerpc/include/uapi/asm/papr_scm_pdsm.h
>> @@ -0,0 +1,134 @@
>> +/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
>> +/*
>> + * PAPR-SCM Dimm specific methods (PDSM) and structs for libndctl
>> + *
>> + * (C) Copyright IBM 2020
>> + *
>> + * Author: Vaibhav Jain <vaibhav at linux.ibm.com>
>> + */
>> +
>> +#ifndef _UAPI_ASM_POWERPC_PAPR_SCM_PDSM_H_
>> +#define _UAPI_ASM_POWERPC_PAPR_SCM_PDSM_H_
>> +
>> +#include <linux/types.h>
>> +
>> +/*
>> + * PDSM Envelope:
>> + *
>> + * The ioctl ND_CMD_CALL transfers data between user-space and kernel via
>> + * 'envelopes' 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 offset of which relative to the struct is provided
>> + * by 'nd_pdsm_cmd_pkg.payload_offset'. *
>> + *
>> + * +-------------+---------------------+---------------------------+
>> + * | 64-Bytes | 8-Bytes | Max 184-Bytes |
>> + * +-------------+---------------------+---------------------------+
>> + * | nd_pdsm_cmd_pkg | |
>> + * |-------------+ | |
>> + * | nd_cmd_pkg | | |
>> + * +-------------+---------------------+---------------------------+
>> + * | nd_family | | |
>> + * | nd_size_out | cmd_status | |
>> + * | nd_size_in | payload_version | PAYLOAD |
>> + * | nd_command | payload_offset -----> |
>> + * | nd_fw_size | | |
>> + * +-------------+---------------------+---------------------------+
>> + *
>> + * 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
>> + * members:
>> + *
>> + * 'cmd_status' : (Out) Errors if any encountered while servicing PDSM.
>> + * 'payload_version' : (In/Out) Version number associated with the payload.
>> + * 'payload_offset' : (In)Relative offset of payload from start of envelope.
>> + *
>> + * 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 184 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.
>
> FWIW many people believe using a size rather than version is more sustainable.
> It is expected that new payload structures are larger (more features) than the
> previous payload structure.
>
> I can't find references at the moment through.
>
> What does payload_version provide us that the command size in/out does
> not?

Taking constrains 1 & 2 mentioned below in section "Backward
Compatibility" into account, there should be a 1:1 mapping between set of
valid 'payload_versions' and set of corrosponding in/out sizes.

However its much more intutive and convenient to figure out the struct
type to use from version number rather than sizes. For example:

struct v1 { u64 a; }; sizeof(v1) == 8
struct v2 { u64 a, b; }; sizeof(v2) == 16

With version numbers its easy to figure out which type to use. However
with in/out size an extra lookup is needed to identify the type to be used.

>
>> + *
>> + * 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 X > Y.
>
> Proper superset? Or Y > X?
>
Good catch. This should be Y > X. Will get this fixed.

> Ira
>
>> + * 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.
>> + */
>> +
>> +/* Papr-scm-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 payload_offset; /* In: offset from start of struct */
>> + __u16 payload_version; /* In/Out: version of the payload */
>> + __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_scm_pdsm {
>> + PAPR_SCM_PDSM_MIN = 0x0,
>> + PAPR_SCM_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 *)((__u8 *) pcmd + pcmd->payload_offset);
>> +}
>> +
>> +#endif /* _UAPI_ASM_POWERPC_PAPR_SCM_PDSM_H_ */
>> diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
>> index 142636e1a59f..ed4b49a6f1e1 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_scm_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 */
>> + 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_SCM) {
>> + 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 */
>> + 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_SCM_PDSM_MIN ||
>> + call_pkg->hdr.nd_command >= PAPR_SCM_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;
>> +
>> + *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;
>> }
>>
>> 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..99fb60600ef8 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_SCM 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