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

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Message-ID: <20241002121330-50b996cf-e296-4f0c-908d-300948728d1f@linutronix.de>
Date: Wed, 2 Oct 2024 12:21:27 +0200
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: Christophe Leroy <christophe.leroy@...roup.eu>
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

Hi Christophe,

On Wed, Oct 02, 2024 at 12:10:08PM GMT, Christophe Leroy wrote:
> Le 02/10/2024 à 10:54, Thomas Weißschuh a écrit :
> > 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.

Ack.

> 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

Yes, it can handle arbitrary arch-specific non-time-related data in
addition to the rng data.
(In addition it also handles arch-specific time-related data)
The code introduced by the linked patch is gone in my series.


Thomas