Hello Marc,
This patch is of special interest to me as I was working on my own
ECV/CNTPOFF implementation, although mine was more narrow and doesn't
address any of your other goals. As far as I can tell at the moment,
your patch can cover the uses of mine, so I will dedicate
myself to reviewing and testing yours. Please include me on any future
rerolls of this patch.
Marc Zyngier <maz@xxxxxxxxxx> writes:
This series aims at satisfying multiple goals:
- allow a VMM to atomically restore a timer offset for a whole VM
instead of updating the offset each time a vcpu get its counter
written
- allow a VMM to save/restore the physical timer context, something
that we cannot do at the moment due to the lack of offsetting
- provide a framework that is suitable for NV support, where we get
both global and per timer, per vcpu offsetting
If I am understanding your changes correctly, you introduce some VM-wide
timers with no hardware backing and a new API to access them from
userspace. This is useful both because it makes the code simpler (no
need to manually keep registers in sync), and so CNT{V,P}OFF can be
appropriately virtualized with NV. Is that a fair summary of the
important bits?
This has been moderately tested with nVHE, VHE and NV. I do not have
access to CNTPOFF-aware HW, so the jury is still out on that one. Note
that the NV patches in this series are here to give a perspective on
how this gets used.
I've updated the arch_timer selftest to allow offsets to be provided
from the command line, but the arch_test is pretty flimsy and tends to
fail with an error==EINTR, even without this series. Something to
investigate.
I can help you with testing because I have access to CNTPOFF-aware
hardware and emulators. Is there anything you are especially interested
to try out?
