On Thu, Feb 20, 2020 at 12:40:47PM +0000, Vincenzo Frascino wrote:

Hi Andrei,

On 04/02/2020 17:59, Andrei Vagin wrote:

quoted

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

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