Subject: Re: [PATCH v5] powerpc/pseries: read the lpar name from the firmware
To:     Laurent Dufour <ldufour@linux.ibm.com>,
        linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Cc:     Nathan Lynch <nathanl@linux.ibm.com>
References: <20220106161339.74656-1-ldufour@linux.ibm.com>
From:   Tyrel Datwyler <tyreld@linux.ibm.com>
Message-ID: <c26f2961-dd19-b888-b601-af5ade74c140@linux.ibm.com>
Date:   Thu, 6 Jan 2022 13:38:02 -0800
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On 1/6/22 8:13 AM, Laurent Dufour wrote:
> The LPAR name may be changed after the LPAR has been started in the HMC.
> In that case lparstat command is not reporting the updated value because it
> reads it from the device tree which is read at boot time.
> 
> However this value could be read from RTAS.
> 
> Adding this value in the /proc/powerpc/lparcfg output allows to read the
> updated value.
> 
> However the hypervisor, like Qemu/KVM, may not support this RTAS
> parameter. In that case the value reported in lparcfg is read from the
> device tree and so is not updated accordingly.
> 
> Cc: Nathan Lynch <nathanl@linux.ibm.com>
> Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>

My only nit would be that in general for consistency with other function names
_RTAS_ and _DT_ should be lowercase. Seeing as they are statically scoped within
lparcfg.c maybe its ok. Otherwise,

Reviewed-by: Tyrel Datwyler <tyreld@linux.ibm.com>

> ---
> v5:
>  fallback to the device tree value if RTAS is not providing the value.
> v4:
>  address Nathan's new comments limiting size of the buffer.
> v3:
>  address Michael's comments.
> v2:
>  address Nathan's comments.
>  change title to partition_name aligning with existing partition_id
> ---
>  arch/powerpc/platforms/pseries/lparcfg.c | 93 ++++++++++++++++++++++++
>  1 file changed, 93 insertions(+)
> 
> diff --git a/arch/powerpc/platforms/pseries/lparcfg.c b/arch/powerpc/platforms/pseries/lparcfg.c
> index c7940fcfc911..8ca08fc306e7 100644
> --- a/arch/powerpc/platforms/pseries/lparcfg.c
> +++ b/arch/powerpc/platforms/pseries/lparcfg.c
> @@ -311,6 +311,98 @@ static void parse_mpp_x_data(struct seq_file *m)
>  		seq_printf(m, "coalesce_pool_spurr=%ld\n", mpp_x_data.pool_spurr_cycles);
>  }
>  
> +/*
> + * PAPR defines, in section "7.3.16 System Parameters Option", the token 55 to
> + * read the LPAR name, and the largest output data to 4000 + 2 bytes length.
> + */
> +#define SPLPAR_LPAR_NAME_TOKEN	55
> +#define GET_SYS_PARM_BUF_SIZE	4002
> +#if GET_SYS_PARM_BUF_SIZE > RTAS_DATA_BUF_SIZE
> +#error "GET_SYS_PARM_BUF_SIZE is larger than RTAS_DATA_BUF_SIZE"
> +#endif
> +
> +/**
> + * Read the lpar name using the RTAS ibm,get-system-parameter call.
> + *
> + * The name read through this call is updated if changes are made by the end
> + * user on the hypervisor side.
> + *
> + * Some hypervisor (like Qemu) may not provide this value. In that case, a non
> + * null value is returned.
> + */
> +static int read_RTAS_lpar_name(struct seq_file *m)
> +{
> +	int rc, len, token;
> +	union {
> +		char raw_buffer[GET_SYS_PARM_BUF_SIZE];
> +		struct {
> +			__be16 len;
> +			char name[GET_SYS_PARM_BUF_SIZE-2];
> +		};
> +	} *local_buffer;
> +
> +	token = rtas_token("ibm,get-system-parameter");
> +	if (token == RTAS_UNKNOWN_SERVICE)
> +		return -EINVAL;
> +
> +	local_buffer = kmalloc(sizeof(*local_buffer), GFP_KERNEL);
> +	if (!local_buffer)
> +		return -ENOMEM;
> +
> +	do {
> +		spin_lock(&rtas_data_buf_lock);
> +		memset(rtas_data_buf, 0, sizeof(*local_buffer));
> +		rc = rtas_call(token, 3, 1, NULL, SPLPAR_LPAR_NAME_TOKEN,
> +			       __pa(rtas_data_buf), sizeof(*local_buffer));
> +		if (!rc)
> +			memcpy(local_buffer->raw_buffer, rtas_data_buf,
> +			       sizeof(local_buffer->raw_buffer));
> +		spin_unlock(&rtas_data_buf_lock);
> +	} while (rtas_busy_delay(rc));
> +
> +	if (!rc) {
> +		/* Force end of string */
> +		len = min((int) be16_to_cpu(local_buffer->len),
> +			  (int) sizeof(local_buffer->name)-1);
> +		local_buffer->name[len] = '\0';
> +
> +		seq_printf(m, "partition_name=%s\n", local_buffer->name);
> +	} else
> +		rc = -ENODATA;
> +
> +	kfree(local_buffer);
> +	return rc;
> +}
> +
> +/**
> + * Read the LPAR name from the Device Tree.
> + *
> + * The value read in the DT is not updated if the end-user is touching the LPAR
> + * name on the hypervisor side.
> + */
> +static int read_DT_lpar_name(struct seq_file *m)
> +{
> +	struct device_node *rootdn;
> +	const char *name;
> +
> +	rootdn = of_find_node_by_path("/");
> +	if (!rootdn)
> +		return -ENOENT;
> +
> +	name = of_get_property(rootdn, "ibm,partition-name", NULL);
> +	if (!name)
> +		return -ENOENT;
> +
> +	seq_printf(m, "partition_name=%s\n", name);
> +	return 0;
> +}
> +
> +static void read_lpar_name(struct seq_file *m)
> +{
> +	if (read_RTAS_lpar_name(m) && read_DT_lpar_name(m))
> +		pr_err_once("Error can't get the LPAR name");
> +}
> +
>  #define SPLPAR_CHARACTERISTICS_TOKEN 20
>  #define SPLPAR_MAXLENGTH 1026*(sizeof(char))
>  
> @@ -496,6 +588,7 @@ static int pseries_lparcfg_data(struct seq_file *m, void *v)
>  
>  	if (firmware_has_feature(FW_FEATURE_SPLPAR)) {
>  		/* this call handles the ibm,get-system-parameter contents */
> +		read_lpar_name(m);
>  		parse_system_parameter_string(m);
>  		parse_ppp_data(m);
>  		parse_mpp_data(m);
>