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

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Message-ID: <20241002104334-b655500b-901b-42db-a2c8-582e10826889@linutronix.de>
Date: Wed, 2 Oct 2024 10:54:23 +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 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.

> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
>  arch/powerpc/include/asm/vdso_datapage.h | 24 +++++++-----------------
>  arch/powerpc/kernel/vdso.c               | 16 ++++++++++------
>  arch/powerpc/kernel/vdso/cacheflush.S    |  2 +-
>  arch/powerpc/kernel/vdso/datapage.S      |  4 ++--
>  arch/powerpc/kernel/vdso/getrandom.S     |  3 +--
>  arch/powerpc/kernel/vdso/gettimeofday.S  |  5 ++---
>  arch/powerpc/kernel/vdso/vdso32.lds.S    |  2 +-
>  arch/powerpc/kernel/vdso/vdso64.lds.S    |  2 +-
>  8 files changed, 25 insertions(+), 33 deletions(-)


Thomas