linux-kernel - Re: [PATCH v7 00/25] Unify vDSOs across more architectures

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Date:   Mon, 24 Jun 2019 14:21:03 +0100
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-arch@...r.kernel.org,
        LAK <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>, linux-mips@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Russell King <linux@...linux.org.uk>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Mark Salyzyn <salyzyn@...roid.com>,
        Peter Collingbourne <pcc@...gle.com>,
        Shuah Khan <shuah@...nel.org>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Huw Davies <huw@...eweavers.com>,
        Shijith Thotton <sthotton@...vell.com>,
        Andre Przywara <andre.przywara@....com>,
        Dmitry Safonov <dima@...sta.com>,
        Andrei Vagin <avagin@...nvz.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH v7 00/25] Unify vDSOs across more architectures

Hi Thomas,

On 24/06/2019 01:34, Thomas Gleixner wrote:
> Vincenzo,
> 
> On Fri, 21 Jun 2019, Vincenzo Frascino wrote:
>> vDSO (virtual dynamic shared object) is a mechanism that the Linux
>> kernel provides as an alternative to system calls to reduce where
>> possible the costs in terms of cycles.
>> This is possible because certain syscalls like gettimeofday() do
>> not write any data and return one or more values that are stored
>> in the kernel, which makes relatively safe calling them directly
>> as a library function.
>>
>> Even if the mechanism is pretty much standard, every architecture
>> in the last few years ended up implementing their own vDSO library
>> in the architectural code.
> 
> ....
>  
>> This implementation contains the portings to the common library for: arm64,
>> compat mode for arm64, arm, mips, x86_64, x32, compat mode for x86_64 and
>> i386.
> 
> I picked up the core implementation and the ARM64 and x86 conversion. I did
> some refinements in several places, coding style, naming conventions,
> comments and changelogs including subject prefixes. Please double check!
>

I tested your changes and they seem OK
(git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git timers/vdso).

...
> As you can see from the commit dates, this has soaked for some time in a
> WIP branch and I did extensive regression testing. So far so good.
> 
> Thanks a lot for going through several iterations. It's a very much
> appreciated effort!
> 

It has been a lot of fun and I learned many many things about the vDSOs and the
kernel that I did not know before. Thanks to you for your patience and guidance.

> Especially with the upcoming time namespaces this will avoid a lot of
> duplicated and pointlessly different horrors all over the architecture
> space. Any architecture which wants to gain that support needs to convert
> to the generic VDSO first.
> 
> As you have become the dude who knows almost everything about VDSO
> including all the nasty pitfalls, I propose the patch below.
>

Thanks for this, it means a lot to me.

> Thanks,
> 
> 	tglx
> 
> 8<------------
> Subject: MAINTAINERS: Add entry for the generic VDSO library
> From: Thomas Gleixner <tglx@...utronix.de>
> Date: Mon, 24 Jun 2019 02:03:50 +0200
> 
> Asign the following folks in alphabetic order:
> 
>  - Andy for being the VDSO wizard of x86 and in general. He's also the
>    performance monitor of choice and the code in the generic library is
>    heavily influenced by his previous x86 VDSO work.
> 
>  - Thomas for being the dude who has to deal with any form of time(r)
>    nonsense anyway
> 
>  - Vincenzo for being the poor sod who went through all the different
>    architecture implementations in order to unify them. A lot of knowledge
>    gained from VDSO implementation details to the intricacies of taming the
>    build system.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  MAINTAINERS |   12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -6665,6 +6665,18 @@ L:	kvm@...r.kernel.org
>  S:	Supported
>  F:	drivers/uio/uio_pci_generic.c
>  
> +GENERIC VDSO LIBRARY:
> +M:	Andy Lutomirksy <luto@...nel.org>
> +M:	Thomas Gleixner <tglx@...utronix.de>
> +M:	Vincenzo Frascino <vincenzo.frascino@....com>
> +L:	linux-kernel@...r.kernel.org
> +T:	git git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git timers/vdso
> +S:	Maintained
> +F:	lib/vdso
> +F:	kernel/time/vsyscall.c
> +F:	include/vdso
> +F:	include/asm-generic/vdso/vsyscall.h
> +
>  GENWQE (IBM Generic Workqueue Card)
>  M:	Frank Haverkamp <haver@...ux.ibm.com>
>  S:	Supported
> 

-- 
Regards,
Vincenzo