Re: [PATCH 04/18] arm64: kernel: add helper for booted at EL2 and not VHE

From: Pavel Tatashin <pasha.tatashin@soleen.com>
To: Marc Zyngier <maz@kernel.org>
Cc: James Morris <jmorris@namei.org>, Sasha Levin <sashal@kernel.org>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	kexec mailing list <kexec@lists.infradead.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Jonathan Corbet <corbet@lwn.net>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	James Morse <james.morse@arm.com>,
	Vladimir Murzin <vladimir.murzin@arm.com>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	linux-mm <linux-mm@kvack.org>,
	Mark Rutland <mark.rutland@arm.com>,
	steve.capper@arm.com, rfontana@redhat.com,
	Thomas Gleixner <tglx@linutronix.de>,
	Selin Dag <selindag@gmail.com>,
	Tyler Hicks <tyhicks@linux.microsoft.com>,
	Pingfan Liu <kernelfans@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	madvenka@linux.microsoft.com
Subject: Re: [PATCH 04/18] arm64: kernel: add helper for booted at EL2 and not VHE
Date: Tue, 1 Jun 2021 21:33:52 -0400	[thread overview]
Message-ID: <CA+CK2bChDqMKGAG8_rEigWcXRaBN=rnuV_WLnU=1TPjJRtpc5A@mail.gmail.com> (raw)
In-Reply-To: <87pmx52212.wl-maz@kernel.org>

On Tue, Jun 1, 2021 at 8:38 AM Marc Zyngier <maz@kernel.org> wrote:
>
> On Thu, 27 May 2021 16:05:12 +0100,
> Pavel Tatashin <pasha.tatashin@soleen.com> wrote:
> >
> > Replace places that contain logic like this:
> >       is_hyp_mode_available() && !is_kernel_in_hyp_mode()
> >
> > With a dedicated boolean function  is_hyp_callable(). This will be needed
> > later in kexec in order to sooner switch back to EL2.
>
> This looks like the very definition of "run in nVHE mode", so I'd
> rather you call it like this, rather than "callable", which is
> extremely ambiguous (if running at EL2, I call it any time I want, for
> free).

Hi Marc,

Naming is hard. Are you proposing  s/is_hyp_callable/run_in_nvhe_mode/
? This is also not a very good name because it does not sound like a
boolean, but instead that we know that there is nvhe mode available
and we can switch to it.

>
> >
> > Suggested-by: James Morse <james.morse@arm.com>
> >
> > [Fixed merging issues]
> >
> > Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
> > ---
> >  arch/arm64/include/asm/virt.h | 5 +++++
> >  arch/arm64/kernel/cpu-reset.h | 3 +--
> >  arch/arm64/kernel/hibernate.c | 9 +++------
> >  arch/arm64/kernel/sdei.c      | 2 +-
> >  4 files changed, 10 insertions(+), 9 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h
> > index 7379f35ae2c6..4216c8623538 100644
> > --- a/arch/arm64/include/asm/virt.h
> > +++ b/arch/arm64/include/asm/virt.h
> > @@ -128,6 +128,11 @@ static __always_inline bool is_protected_kvm_enabled(void)
> >               return cpus_have_final_cap(ARM64_KVM_PROTECTED_MODE);
> >  }
> >
> > +static inline bool is_hyp_callable(void)
> > +{
> > +     return is_hyp_mode_available() && !is_kernel_in_hyp_mode();
> > +}
>
> nit: consider switching the two members of the expression so that you
> don't have extra memory accesses when running at EL2.

Sure, I will do that.

> > -/* Do we need to reset el2? */
> > -#define el2_reset_needed() (is_hyp_mode_available() && !is_kernel_in_hyp_mode())
> > -
>
> Please keep the macro, as it explains *why* we're doing things (we
> need to reset EL2), and replacing it with a generic macro drops the
> documentation aspect.

OK, I will keep the macro, and redefine it to use the common macro.

Thank you,
Pasha