linux-kernel - Re: [RFC PATCH v2 11/26] KVM: arm64: Stub CONFIG_DEBUG

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Date:   Tue, 2 Feb 2021 10:00:29 +0000
From:   Will Deacon <will@...nel.org>
To:     Quentin Perret <qperret@...gle.com>
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 11/26] KVM: arm64: Stub CONFIG_DEBUG_LIST at Hyp

On Tue, Feb 02, 2021 at 09:57:36AM +0000, Quentin Perret wrote:
> On Monday 01 Feb 2021 at 19:06:20 (+0000), Will Deacon wrote:
> > On Fri, Jan 08, 2021 at 12:15:09PM +0000, Quentin Perret wrote:
> > > In order to use the kernel list library at EL2, introduce stubs for the
> > > CONFIG_DEBUG_LIST out-of-lines calls.
> > > 
> > > Signed-off-by: Quentin Perret <qperret@...gle.com>
> > > ---
> > >  arch/arm64/kvm/hyp/nvhe/Makefile |  2 +-
> > >  arch/arm64/kvm/hyp/nvhe/stub.c   | 22 ++++++++++++++++++++++
> > >  2 files changed, 23 insertions(+), 1 deletion(-)
> > >  create mode 100644 arch/arm64/kvm/hyp/nvhe/stub.c
> > > 
> > > diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile
> > > index 1fc0684a7678..33bd381d8f73 100644
> > > --- a/arch/arm64/kvm/hyp/nvhe/Makefile
> > > +++ b/arch/arm64/kvm/hyp/nvhe/Makefile
> > > @@ -10,7 +10,7 @@ lib-objs := clear_page.o copy_page.o memcpy.o memset.o
> > >  lib-objs := $(addprefix ../../../lib/, $(lib-objs))
> > >  
> > >  obj-y := timer-sr.o sysreg-sr.o debug-sr.o switch.o tlb.o hyp-init.o host.o \
> > > -	 hyp-main.o hyp-smp.o psci-relay.o early_alloc.o
> > > +	 hyp-main.o hyp-smp.o psci-relay.o early_alloc.o stub.o
> > >  obj-y += ../vgic-v3-sr.o ../aarch32.o ../vgic-v2-cpuif-proxy.o ../entry.o \
> > >  	 ../fpsimd.o ../hyp-entry.o ../exception.o
> > >  obj-y += $(lib-objs)
> > > diff --git a/arch/arm64/kvm/hyp/nvhe/stub.c b/arch/arm64/kvm/hyp/nvhe/stub.c
> > > new file mode 100644
> > > index 000000000000..c0aa6bbfd79d
> > > --- /dev/null
> > > +++ b/arch/arm64/kvm/hyp/nvhe/stub.c
> > > @@ -0,0 +1,22 @@
> > > +// SPDX-License-Identifier: GPL-2.0-only
> > > +/*
> > > + * Stubs for out-of-line function calls caused by re-using kernel
> > > + * infrastructure at EL2.
> > > + *
> > > + * Copyright (C) 2020 - Google LLC
> > > + */
> > > +
> > > +#include <linux/list.h>
> > > +
> > > +#ifdef CONFIG_DEBUG_LIST
> > > +bool __list_add_valid(struct list_head *new, struct list_head *prev,
> > > +		      struct list_head *next)
> > > +{
> > > +		return true;
> > > +}
> > > +
> > > +bool __list_del_entry_valid(struct list_head *entry)
> > > +{
> > > +		return true;
> > > +}
> > > +#endif
> > 
> > Can we get away with defining our own CHECK_DATA_CORRUPTION macro instead?
> 
> Yes I think eventually it'd be nice to get there, but that has other
> implications (e.g. how do you report something in dmesg from EL2?) so
> perhaps we can keep that a separate series?

We wouldn't necessarily have to report anything, but having the return value
of these functions be based off the generic checks would be great if we can
do it (i.e. we'd avoid corrupting the list).

Will