[PATCH v6 17/21] KVM: arm64: Allow userspace to configure a guest's counter-timer offset

[Marc Zyngier]

On Tue, 10 Aug 2021 18:55:12 +0100,
Oliver Upton <oupton at google.com> wrote:
> 
> On Tue, Aug 10, 2021 at 3:56 AM Marc Zyngier <maz at kernel.org> wrote:
> >
> > On Wed, 04 Aug 2021 09:58:15 +0100,
> > Oliver Upton <oupton at google.com> wrote:

[...]

> > > diff --git a/include/clocksource/arm_arch_timer.h b/include/clocksource/arm_arch_timer.h
> > > index 73c7139c866f..7252ffa3d675 100644
> > > --- a/include/clocksource/arm_arch_timer.h
> > > +++ b/include/clocksource/arm_arch_timer.h
> > > @@ -21,6 +21,7 @@
> > >  #define CNTHCTL_EVNTEN                       (1 << 2)
> > >  #define CNTHCTL_EVNTDIR                      (1 << 3)
> > >  #define CNTHCTL_EVNTI                        (0xF << 4)
> > > +#define CNTHCTL_ECV                  (1 << 12)
> > >
> > >  enum arch_timer_reg {
> > >       ARCH_TIMER_REG_CTRL,
> >
> > You also want to document that SCR_EL3.ECVEn has to be set to 1 for
> > this to work (see Documentation/arm64/booting.txt). And if it isn't,
> > the firmware better handle the CNTPOFF_EL2 traps correctly...
> 
> I'll grab the popcorn now ;-) Adding docs for this, good idea.
> 
> > What firmware did you use for this? I think we need to update the boot
> > wrapper, but that's something that can be done in parallel.
> 
> I had actually just done a direct boot from ARM-TF -> Linux, nothing
> else in between.

Ah, right. I tend to use the boot-wrapper[1] to build a single binary
that contains the 'boot loader', DT and kernel. Using ATF is probably
more representative of the final thing, but the boot-wrapper is dead
easy to hack on...

Thanks,

	M.

[1] git://git.kernel.org/pub/scm/linux/kernel/git/mark/boot-wrapper-aarch64.git

-- 
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