Re: [PATCH v3 21/28] cxl/pmem: Translate NVDIMM label commands to CXL label commands

[Dan Williams <dan.j.williams@intel.com>]

On Thu, Sep 2, 2021 at 11:22 AM Jonathan Cameron
<Jonathan.Cameron@huawei.com> wrote:
>
> On Tue, 24 Aug 2021 09:07:18 -0700
> Dan Williams <dan.j.williams@intel.com> wrote:
>
> > The LIBNVDIMM IOCTL UAPI calls back to the nvdimm-bus-provider to
> > translate the Linux command payload to the device native command format.
> > The LIBNVDIMM commands get-config-size, get-config-data, and
> > set-config-data, map to the CXL memory device commands device-identify,
> > get-lsa, and set-lsa. Recall that the label-storage-area (LSA) on an
> > NVDIMM device arranges for the provisioning of namespaces. Additionally
> > for CXL the LSA is used for provisioning regions as well.
> >
> > The data from device-identify is already cached in the 'struct cxl_mem'
> > instance associated with @cxl_nvd, so that payload return is simply
> > crafted and no CXL command is issued. The conversion for get-lsa is
> > straightforward, but the conversion for set-lsa requires an allocation
> > to append the set-lsa header in front of the payload.
> >
> > Acked-by: Ben Widawsky <ben.widawsky@intel.com>
> > Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> Minor query inline.
>
[..]
> > +static int cxl_pmem_set_config_data(struct cxl_mem *cxlm,
> > +                                 struct nd_cmd_set_config_hdr *cmd,
> > +                                 unsigned int buf_len, int *cmd_rc)
> > +{
> > +     struct cxl_mbox_set_lsa {
> > +             u32 offset;
> > +             u32 reserved;
> > +             u8 data[];
> > +     } *set_lsa;
> > +     int rc;
> > +
> > +     if (sizeof(*cmd) > buf_len)
> > +             return -EINVAL;
> > +
> > +     /* 4-byte status follows the input data in the payload */
> > +     if (struct_size(cmd, in_buf, cmd->in_length) + 4 > buf_len)
> > +             return -EINVAL;
> > +
> > +     set_lsa =
> > +             kvzalloc(struct_size(set_lsa, data, cmd->in_length), GFP_KERNEL);
> > +     if (!set_lsa)
> > +             return -ENOMEM;
> > +
> > +     *set_lsa = (struct cxl_mbox_set_lsa) {
> > +             .offset = cmd->in_offset,
> > +     };
> > +     memcpy(set_lsa->data, cmd->in_buf, cmd->in_length);
> > +
> > +     rc = cxl_mem_mbox_send_cmd(cxlm, CXL_MBOX_OP_SET_LSA, set_lsa,
> > +                                struct_size(set_lsa, data, cmd->in_length),
> > +                                NULL, 0);
> > +
> > +     /* set "firmware" status */
> > +     *(u32 *) &cmd->in_buf[cmd->in_length] = 0;
>
> Are we guaranteed this is aligned? Not 'locally' obvious so maybe a comment?

Good point, let's just go ahead and use a put_unaligned() accessor.