linux-kernel - Re: [PATCH 1/2] powerpc/vdso: Add a page for non-time data

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Message-ID: <368e38d3-5883-4192-b9cf-f66d0f558528@csgroup.eu>
Date: Wed, 2 Oct 2024 12:10:08 +0200
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Cc: Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin
 <npiggin@...il.com>, Naveen N Rao <naveen@...nel.org>,
 linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org, Jason@...c4.com
Subject: Re: [PATCH 1/2] powerpc/vdso: Add a page for non-time data



Le 02/10/2024 à 10:54, Thomas Weißschuh a écrit :
> [Vous ne recevez pas souvent de courriers de thomas.weissschuh@...utronix.de. D?couvrez pourquoi ceci est important ? https://aka.ms/LearnAboutSenderIdentification ]
> 
> Hi Christophe,
> 
> On Wed, Oct 02, 2024 at 10:39:28AM GMT, Christophe Leroy wrote:
>> The page containing VDSO time data is swapped with the one containing
>> TIME namespace data when a process uses a non-root time namespace.
>> For other data like powerpc specific data and RNG data, it means
>> tracking whether time namespace is the root one or not to know which
>> page to use.
>>
>> Simplify the logic behind by moving time data out of first data page
>> so that the first data page which contains everything else always
>> remains the first page. Time data is in the second or third page
>> depending on selected time namespace.
>>
>> While we are playing with get_datapage macro, directly take into
>> account the data offset inside the macro instead of adding that offset
>> afterwards.
> 
> FYI
> 
> I am currently working on a series to unify the storage of the
> VDSO data for most architectures, including powerpc.
> This will also include a dedicated rng data page.
> 
> That generic infrastructure would replace the need for Patch 1.
> Obviously, if your series gets applied, I can adapt mine for that.
> 
> If you are about to also modify other architectures in a similar way,
> we may want to coordinate.
> 

I'm not going to do anything on other architectures.

Indeed my patch is an outcome of the discussion at 
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/ffd7fc255e194d1e2b0aa3d9d129e826c53219d4.1725611321.git.christophe.leroy@csgroup.eu/

I'm all fine if you are doing something generic for all architectures. 
For powerpc will it handle the entire non-time data, not only rng ? The 
purpose being to revert 
https://github.com/torvalds/linux/commit/c73049389e58c01e2e3bbfae900c8daeee177191

Christophe