linux-kernel - Re: [PATCH 5/5] arm64: Document the requirement for SCR

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Date:   Tue, 24 Aug 2021 11:52:02 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Marc Zyngier <maz@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Rafał Miłecki <zajec5@...il.com>,
        Will Deacon <will@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        bcm-kernel-feedback-list@...adcom.com, kernel-team@...roid.com
Subject: Re: [PATCH 5/5] arm64: Document the requirement for SCR_EL3.HCE

On Tue, Aug 24, 2021 at 11:49:01AM +0100, Catalin Marinas wrote:
> On Thu, Aug 12, 2021 at 08:02:13PM +0100, Marc Zyngier wrote:
> > It is amazing that we never documented this absolutely basic
> > requirement: if you boot the kernel at EL2, you'd better
> > enable the HVC instruction from EL3.
> > 
> > Really, just do it.
> > 
> > Signed-off-by: Marc Zyngier <maz@...nel.org>
> > ---
> >  Documentation/arm64/booting.rst | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/Documentation/arm64/booting.rst b/Documentation/arm64/booting.rst
> > index a9192e7a231b..6c729d0c4bc2 100644
> > --- a/Documentation/arm64/booting.rst
> > +++ b/Documentation/arm64/booting.rst
> > @@ -212,6 +212,11 @@ Before jumping into the kernel, the following conditions must be met:
> >    - The value of SCR_EL3.FIQ must be the same as the one present at boot
> >      time whenever the kernel is executing.
> >  
> > +  For all systems:
> > +  - If EL3 is present and the kernel is entered at EL2:
> > +
> > +    - SCR_EL3.HCE (bit 8) must be initialised to 0b1.
> > +
> >    For systems with a GICv3 interrupt controller to be used in v3 mode:
> >    - If EL3 is present:
> 
> I'll queue this patch only for now.
> 
> A nitpick, I think we should move "For all systems" and "If EL3 is
> present..." above the lines describing the SCR_EL3.FIQ requirement (I
> can make the change locally).


FWIW, with that:

Acked-by: Mark Rutland <mark.rutland@....com>

Mark.