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

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Date:   Sun, 23 Feb 2020 00:08:11 -0800
From:   Andrei Vagin <avagin@...il.com>
To:     Vincenzo Frascino <vincenzo.frascino@....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

On Thu, Feb 20, 2020 at 12:40:47PM +0000, Vincenzo Frascino wrote:
> Hi Andrei,
> 
> On 04/02/2020 17:59, 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.
> > 
> 
> Thank you for adding the arm64 support of time namespaces. Overall it looks fine
> to me even if I have few comments. I will test it in the coming days just to
> make sure I did not miss something major. I will keep you updated on the results.

Thank you for the review. All comments look reasonable and I will
address them and post a second version.

Thanks,
Andrei