Re: [PATCH 11/14] arm64: dts: Add initial device tree support for EXYNOS7

[Mark Rutland <mark.rutland@arm.com>]

On Thu, Aug 28, 2014 at 06:37:19PM +0100, Marc Zyngier wrote:
> On 28/08/14 18:30, Mark Rutland wrote:
> > On Thu, Aug 28, 2014 at 06:27:04PM +0100, Marc Zyngier wrote:
> >> On 28/08/14 18:03, Mark Rutland wrote:
> >>
> >>> From 67104ad5a56e4c18f9c41f06af028b7561740afd Mon Sep 17 00:00:00 2001
> >>> From: Mark Rutland <mark.rutland@arm.com>
> >>> Date: Thu, 28 Aug 2014 17:41:03 +0100
> >>> Subject: [PATCH] Doc: dt: arch_timer: discourage clock-frequency use
> >>>
> >>> The ARM Generic Timer (AKA the architected timer, arm_arch_timer)
> >>> features a CPU register (CNTFRQ) which firmware is intended to
> >>> initialize, and non-secure software can read to determine the frequency
> >>> of the timer. On CPUs with secure state, this register cannot be written
> >>> from non-secure states.
> >>>
> >>> The firmware of early SoCs featuring the timer did not correctly
> >>> initialize CNTFRQ correctly on all CPUs, requiring the frequency to be
> >>> described in DT as a workaround. This workaround is not complete however
> >>> as CNTFRQ is exposed to all software in a privileged non-secure mode,
> >>> including KVM guests. The firmware and DTs for recent SoCs have followed
> >>
> >> I believe Xen is also affected by this.
> > 
> > True.
> > 
> > s/KVM/KVM\/Xen/, then?
> 
> Yup. Or "including guests running under a hypervisor"

Ah, that sounds better. I'll use that for the next posting.

> I expect this to be such a fundamental problem that all hypervisors
> will trip over on that one (Jailhouse definitely does).

Yeah, this is a generic problem.

Mark.