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

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Message-ID: <da130af8-5434-0768-661f-7a6a7e417567@linux.ibm.com>
Date:   Thu, 6 Jan 2022 10:17:48 +0100
From:   Laurent Dufour <ldufour@...ux.ibm.com>
To:     Tyrel Datwyler <tyreld@...ux.ibm.com>,
        Nathan Lynch <nathanl@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] powerpc/pseries: read the lpar name from the firmware

On 06/01/2022, 02:17:21, Tyrel Datwyler wrote:
> 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.
> 
>>
>> 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.

My aim is to not do in the kernel what can be easily done in user space but
avoiding user space program hypervisor-specific branches is a good point.

Note that if the RTAS call has been available to unprivileged user, all
that stuff would have been made in user space, so hypervisor-specific...

Anyway, I'll work on a new version fetching the DT value in the case the
RTAS call is failing.

Thanks,
Laurent.