linux-kernel - Re: [RFC PATCH v2 03/26] arm64: kvm: Add standalone ticket spinlock implementation for use at hyp

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Message-ID: <YBg9KPnKfJzraTBO@google.com>
Date:   Mon, 1 Feb 2021 17:40:56 +0000
From:   Quentin Perret <qperret@...gle.com>
To:     Will Deacon <will@...nel.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        devicetree@...r.kernel.org, android-kvm@...gle.com,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
        Fuad Tabba <tabba@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        David Brazdil <dbrazdil@...gle.com>
Subject: Re: [RFC PATCH v2 03/26] arm64: kvm: Add standalone ticket spinlock
 implementation for use at hyp

On Monday 01 Feb 2021 at 17:28:34 (+0000), Will Deacon wrote:
> On Fri, Jan 08, 2021 at 12:15:01PM +0000, Quentin Perret wrote:
> > From: Will Deacon <will@...nel.org>
> > 
> > We will soon need to synchronise multiple CPUs in the hyp text at EL2.
> > The qspinlock-based locking used by the host is overkill for this purpose
> > and relies on the kernel's "percpu" implementation for the MCS nodes.
> > 
> > Implement a simple ticket locking scheme based heavily on the code removed
> > by commit c11090474d70 ("arm64: locking: Replace ticket lock implementation
> > with qspinlock").
> > 
> > Signed-off-by: Will Deacon <will@...nel.org>
> > Signed-off-by: Quentin Perret <qperret@...gle.com>
> > ---
> >  arch/arm64/kvm/hyp/include/nvhe/spinlock.h | 92 ++++++++++++++++++++++
> >  1 file changed, 92 insertions(+)
> >  create mode 100644 arch/arm64/kvm/hyp/include/nvhe/spinlock.h
> > 
> > diff --git a/arch/arm64/kvm/hyp/include/nvhe/spinlock.h b/arch/arm64/kvm/hyp/include/nvhe/spinlock.h
> > new file mode 100644
> > index 000000000000..7584c397bbac
> > --- /dev/null
> > +++ b/arch/arm64/kvm/hyp/include/nvhe/spinlock.h
> > @@ -0,0 +1,92 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +/*
> > + * A stand-alone ticket spinlock implementation for use by the non-VHE
> > + * KVM hypervisor code running at EL2.
> > + *
> > + * Copyright (C) 2020 Google LLC
> > + * Author: Will Deacon <will@...nel.org>
> > + *
> > + * Heavily based on the implementation removed by c11090474d70 which was:
> > + * Copyright (C) 2012 ARM Ltd.
> > + */
> > +
> > +#ifndef __ARM64_KVM_NVHE_SPINLOCK_H__
> > +#define __ARM64_KVM_NVHE_SPINLOCK_H__
> > +
> > +#include <asm/alternative.h>
> > +#include <asm/lse.h>
> > +
> > +typedef union hyp_spinlock {
> > +	u32	__val;
> > +	struct {
> > +#ifdef __AARCH64EB__
> > +		u16 next, owner;
> > +#else
> > +		u16 owner, next;
> > +	};
> > +#endif
> 
> Looks like I put this #endif in the wrong place; probably needs to be a line
> higher.

Uh oh, missed that too. Fix now merged locally, thanks.

Quentin