On 07/12/2021, 15:32:39, Nathan Lynch wrote:
> Hi Laurent,
>
> Laurent Dufour <lduf...@linux.ibm.com> writes:
>> +/*
>> + * PAPR defines, in section "7.3.16 System Parameters Option", the token 55
>> to
>> + * read the LPAR name.
>> + */
>> +#define SPLPAR_LPAR_NAME_TOKEN 55
>> +static void read_lpar_name(struct seq_file *m)
>> +{
>> + int rc, len, token;
>> + union {
>> + char raw_buffer[RTAS_DATA_BUF_SIZE];
>> + struct {
>> + __be16 len;
>
> This:
>
>> + char name[RTAS_DATA_BUF_SIZE-2];
> ^^^^^^
>
> should be 4000, not (4K - 2), according to PAPR (it's weird and I don't
> know the reason).
That's true, PAPR defines the largest output buffer for
ibm,get-system-parameter to 4002, so we could limit this to 4002, not sure
whether this would make a big difference here. Anyway I will limit that
buffer size this way.
>
>
>> + };
>> + } *local_buffer;
>> +
>> + token = rtas_token("ibm,get-system-parameter");
>> + if (token == RTAS_UNKNOWN_SERVICE)
>> + return;
>> +
>> + local_buffer = kmalloc(sizeof(*local_buffer), GFP_KERNEL);
>> + if (!local_buffer)
>> + return;
>> +
>> + do {
>> + spin_lock(&rtas_data_buf_lock);
>> + memset(rtas_data_buf, 0, RTAS_DATA_BUF_SIZE);
>> + rc = rtas_call(token, 3, 1, NULL, SPLPAR_LPAR_NAME_TOKEN,
>> + __pa(rtas_data_buf), RTAS_DATA_BUF_SIZE);
>> + if (!rc)
>> + memcpy(local_buffer->raw_buffer, rtas_data_buf,
>> + RTAS_DATA_BUF_SIZE);
>> + spin_unlock(&rtas_data_buf_lock);
>> + } while (rtas_busy_delay(rc));
>> +
>> + if (rc != 0) {
>> + pr_err_once(
>> + "%s %s Error calling get-system-parameter (0x%x)\n",
>> + __FILE__, __func__, rc);
>
> The __FILE__ and __func__ in the message seem unnecessary, and rc should
> be reported in decimal so the error meaning is apparent.
Fair enough.
> Is there a reasonable fallback for VMs where this parameter doesn't
> exist? PowerVM partitions should always have it, but what do we want the
> behavior to be on other hypervisors?
In that case, there is no value displayed in the /proc/powerpc/lparcfg and
the lparstat -i command will fall back to the device tree value. I can't
see any valid reason to report the value defined in the device tree here.
>
>
>> + } else {
>> + /* Force end of string */
>> + len = be16_to_cpu(local_buffer->len);
>> + if (len >= (RTAS_DATA_BUF_SIZE-2))
>> + len = RTAS_DATA_BUF_SIZE-2;
>
> Could use min() or clamp(), and it would be better to build the
> expression using the value of sizeof(local_buffer->name).
Fair enough.
>
>> + local_buffer->name[len] = '\0';
>
> If 'len' can be (RTAS_DATA_BUF_SIZE - 2), then this writes past the end
> of the buffer, no?
Oh yes, the previous test should be
if (len >= (RTAS_DATA_BUF_SIZE-2))
len = RTAS_DATA_BUF_SIZE-3;
Thanks,
Laurent.
