linux-kernel - Re: [PATCH 0/5] arm64: add the time namespace support

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Date:   Mon, 17 Feb 2020 18:25:08 +0000
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     Andrei Vagin <avagin@...il.com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Safonov <dima@...sta.com>
Subject: Re: [PATCH 0/5] arm64: add the time namespace support

Hi Andrei,

On 17/02/2020 15:34, Andrei Vagin wrote:
> Vincenzo, could you take a look this patchset?
> 

Apologize for not getting to this yet. I will have a look at your patches during
this week.

> On Tue, Feb 04, 2020 at 09:59:08AM -0800, 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.
>>
>> Cc: Vincenzo Frascino <vincenzo.frascino@....com>
>> Cc: Thomas Gleixner <tglx@...utronix.de>
>> Cc: Dmitry Safonov <dima@...sta.com>
>>
>> Andrei Vagin (5):
>>   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
>>
>>  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
>>

-- 
Regards,
Vincenzo

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