Re: [PATCH v2 0/3] KVM: arm64: Fixes for timers and pKVM

[Marc Zyngier]

On Tue, 11 Aug 2026 13:17:25 +0100,
Mostafa Saleh <smostafa@xxxxxxxxxx> wrote:
> 
> On Sat, Aug 8, 2026 at 7:44 PM Oliver Upton <oupton@xxxxxxxxxx> wrote:
> >
> > On Sat, 08 Aug 2026 08:58:21 +0000, Mostafa Saleh wrote:
> > > What started as a  small patch ended up as a 3 patch series thanks
> > > to Sashiko.
> > >
> > > First patch from Marc to consolidate the offset calculation,
> > > follow up patches fix issues with non-protected VM and timer
> > > offset and protected VM running with broken CNTVOFF_EL2.
> > >
> > > [...]
> >
> > Dropped the unintended SOB in patch 3 you mentioned.
> >
> > Applied to next, thanks!
> >
> > [1/3] KVM: arm64: Make timer_get_offset() work in all contexts
> >       https://git.kernel.org/kvmarm/kvmarm/c/2858600ecd01
> > [2/3] KVM: arm64: Fix timer offsets for non-protected VMs
> >       https://git.kernel.org/kvmarm/kvmarm/c/47d3eef780e3
> > [3/3] KVM: arm64: Fix hvhe and broken CNTVOFF_EL2
> >       https://git.kernel.org/kvmarm/kvmarm/c/2e813a6e8ebe
> >
> 
> Thanks Oliver! I believe there is one more bug. I'm not sure where the
> bug is or if it relates to the broken timers.
> Before those patches I could not boot a protected VM because of the
> panic, now after booting protected VMs, I sometimes get a system
> reset.

On this quality HW, this is usually an indication that you are taking
an exception in a tight loop.

> I confirmed that cntvoff_el2 does not get written to non-zero, I also
> removed the sysreg write completely (rely on xzr value at init) so my
> guess is that the HW might be allergic to more than just non-zero
> values in cntvoff_el2.

Is that in hVHE mode? Can you trap the access and route it to the
existing handling code?

> I do not have issues with non-protected VMs anymore.

Do these run with an offset or not?

	M.

-- 
Without deviation from the norm, progress is not possible.