linux-kernel - Re: [PATCH v4] powerpc/pseries: read the lpar name from the firmware

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Date:   Wed, 05 Jan 2022 19:36:03 -0600
From:   Nathan Lynch <nathanl@...ux.ibm.com>
To:     Tyrel Datwyler <tyreld@...ux.ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH v4] powerpc/pseries: read the lpar name from the firmware

Tyrel Datwyler <tyreld@...ux.ibm.com> writes:
> On 1/5/22 3:19 PM, Nathan Lynch wrote:
>> Laurent Dufour <ldufour@...ux.ibm.com> writes:
>>> On 07/12/2021, 18:11:09, 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.
>>>
>>> Do you consider taking that patch soon?
>> 
>> This version prints an error on non-PowerVM guests the first time
>> lparcfg is read.
>
> I assume because QEMU doesn't implement the LPAR_NAME token for
> get_sysparm.

Correct.


>> And I still contend that having this function fall back to reporting the
>> partition name in the DT would provide a beneficial consistency in the
>> user-facing API, allowing programs to avoid hypervisor-specific branches
>> in their code. 
>
> Agreed, if the get_sysparm fails just report the lpar-name from the device tree.
>
>> I don't understand the resistance I've encountered here.
>> The fallback I'm suggesting (a root node property lookup) is certainly
>> not more complex than the RTAS call sequence you've already implemented.
>> 
>
> Is there benefit of adding a partition_name field/value pair to lparcfg? The
> lparstat utility can just as easily make the get_sysparm call via librtas.
> Further, rtas_filters allows this particular RTAS call from userspace.

The RTAS syscall is root-only, but we want the partition name (whether
supplied by RTAS or the device tree) to be available to unprivileged
programs.