linux-kernel - Re: [PATCH RESEND v3 0/6] arm64: add the time namespace support

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Date:   Fri, 5 Jun 2020 11:49:04 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Andrei Vagin <avagin@...il.com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Safonov <dima@...sta.com>
Subject: Re: [PATCH RESEND v3 0/6] arm64: add the time namespace support

Hi Andrei,

As a heads up, in mainline the arm64 vdso code has been refactored since
v5.7, and this series will need to be rebased atop. Given we're in the
middle of the merge window, I would suggest waiting until rc1 before
posting a rebased series.

In the meantime, the relevant patches can be found in arm64's for-next/core
branch:

git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-next/core

... which was merged into mainline in commit:

  533b220f7be4e461 ("Merge tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux")

Thanks,
Mark.

On Tue, Jun 02, 2020 at 11:02:53AM -0700, Andrei Vagin wrote:
> Allocate the time namespace page among VVAR pages and add the logic
> to handle faults on VVAR properly.
> 
> If a task belongs to a time namespace then the VVAR page which contains
> the system wide VDSO data is replaced with a namespace specific page
> which has the same layout as the VVAR page. That page has vdso_data->seq
> set to 1 to enforce the slow path and vdso_data->clock_mode set to
> VCLOCK_TIMENS to enforce the time namespace handling path.
> 
> The extra check in the case that vdso_data->seq is odd, e.g. a concurrent
> update of the VDSO data is in progress, is not really affecting regular
> tasks which are not part of a time namespace as the task is spin waiting
> for the update to finish and vdso_data->seq to become even again.
> 
> If a time namespace task hits that code path, it invokes the corresponding
> time getter function which retrieves the real VVAR page, reads host time
> and then adds the offset for the requested clock which is stored in the
> special VVAR page.
> 
> v2: Code cleanups suggested by Vincenzo.
> v3: add a comment in __arch_get_timens_vdso_data.
> 
> Reviewed-by: Vincenzo Frascino <vincenzo.frascino@....com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Dmitry Safonov <dima@...sta.com>
> 
> v3 on github (if someone prefers `git pull` to `git am`):
> https://github.com/avagin/linux-task-diag/tree/arm64/timens-v3
> 
> Andrei Vagin (6):
>   arm64/vdso: use the fault callback to map vvar pages
>   arm64/vdso: Zap vvar pages when switching to a time namespace
>   arm64/vdso: Add time napespace page
>   arm64/vdso: Handle faults on timens page
>   arm64/vdso: Restrict splitting VVAR VMA
>   arm64: enable time namespace support
> 
>  arch/arm64/Kconfig                            |   1 +
>  .../include/asm/vdso/compat_gettimeofday.h    |  11 ++
>  arch/arm64/include/asm/vdso/gettimeofday.h    |   8 ++
>  arch/arm64/kernel/vdso.c                      | 134 ++++++++++++++++--
>  arch/arm64/kernel/vdso/vdso.lds.S             |   3 +-
>  arch/arm64/kernel/vdso32/vdso.lds.S           |   3 +-
>  include/vdso/datapage.h                       |   1 +
>  7 files changed, 147 insertions(+), 14 deletions(-)
> 
> -- 
> 2.24.1
>