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Subject: Re: [PATCH v2 0/6] arm64: add the time namespace support
To:     Andrei Vagin <avagin@gmail.com>
Cc:     linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Thomas Gleixner <tglx@linutronix.de>,
        Dmitry Safonov <dima@arista.com>
References: <20200225073731.465270-1-avagin@gmail.com>
From:   Vincenzo Frascino <vincenzo.frascino@arm.com>
Message-ID: <1c1ab662-5475-9d8b-038b-8411b060202a@arm.com>
Date:   Thu, 9 Apr 2020 14:24:39 +0100
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Hi Andrei,

On 2/25/20 7:37 AM, 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.
> 

Sorry for the delay, I completed this morning the review of your patches and I
do not have anymore comments on them. Thank you for making the effort and
bringing the time namespace support to arm64.

I have though a question on something I encountered during the testing of the
patches: I noticed that all the tests related to CLOCK_BOOTTIME_ALARM fail on
arm64 (please find the results below the scissors). Is this expected?

--->8---

1..4
ok 1 clockid: 1 abs:0
ok 2 clockid: 1 abs:1
not ok 3 # error clock_gettime: Invalid argument
not ok 4 # error clock_gettime: Invalid argument
Bail out!
# Pass 2 Fail 0 Xfail 0 Xpass 0 Skip 0 Error 2
1..1
ok 1 exec
# Pass 1 Fail 0 Xfail 0 Xpass 0 Skip 0 Error 0
1..8
not ok 1 # error Warning: failed to find clock_gettime in vDSO

./timens.sh: line 5: 15382 Segmentation fault      (core dumped) ./gettime_perf
1..1
ok 1 Passed for /proc/uptime
# Pass 1 Fail 0 Xfail 0 Xpass 0 Skip 0 Error 0
1..10
ok 1 Passed for CLOCK_BOOTTIME (syscall)
ok 2 Passed for CLOCK_BOOTTIME (vdso)
not ok 3 # error syscall(SYS_clock_gettime(9)): Invalid argument
not ok 4 # error clock_gettime(9): Invalid argument
ok 5 Passed for CLOCK_MONOTONIC (syscall)
ok 6 Passed for CLOCK_MONOTONIC (vdso)
ok 7 Passed for CLOCK_MONOTONIC_COARSE (syscall)
ok 8 Passed for CLOCK_MONOTONIC_COARSE (vdso)
ok 9 Passed for CLOCK_MONOTONIC_RAW (syscall)
ok 10 Passed for CLOCK_MONOTONIC_RAW (vdso)
Bail out!
# Pass 8 Fail 0 Xfail 0 Xpass 0 Skip 0 Error 2
1..3
ok 1 clockid=7
ok 2 clockid=1
not ok 3 # error timerfd_create: Operation not supported
Bail out!
# Pass 2 Fail 0 Xfail 0 Xpass 0 Skip 0 Error 1
1..3
ok 1 clockid=7
ok 2 clockid=1
ok 3 clockid=9
# Pass 3 Fail 0 Xfail 0 Xpass 0 Skip 0 Error 0

[...]

-- 
Regards,
Vincenzo