linux-kernel - Re: [PATCH v5 14/36] KVM: arm64: Provide __flush_dcache

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Message-ID: <20210315170310.GI3430@willie-the-truck>
Date:   Mon, 15 Mar 2021 17:03:10 +0000
From:   Will Deacon <will@...nel.org>
To:     Quentin Perret <qperret@...gle.com>
Cc:     catalin.marinas@....com, maz@...nel.org, james.morse@....com,
        julien.thierry.kdev@...il.com, suzuki.poulose@....com,
        android-kvm@...gle.com, seanjc@...gle.com, mate.toth-pal@....com,
        linux-kernel@...r.kernel.org, robh+dt@...nel.org,
        linux-arm-kernel@...ts.infradead.org, kernel-team@...roid.com,
        kvmarm@...ts.cs.columbia.edu, tabba@...gle.com, ardb@...nel.org,
        mark.rutland@....com, dbrazdil@...gle.com
Subject: Re: [PATCH v5 14/36] KVM: arm64: Provide __flush_dcache_area at EL2

On Mon, Mar 15, 2021 at 04:56:21PM +0000, Quentin Perret wrote:
> On Monday 15 Mar 2021 at 16:33:23 (+0000), Will Deacon wrote:
> > On Mon, Mar 15, 2021 at 02:35:14PM +0000, Quentin Perret wrote:
> > > We will need to do cache maintenance at EL2 soon, so compile a copy of
> > > __flush_dcache_area at EL2, and provide a copy of arm64_ftr_reg_ctrel0
> > > as it is needed by the read_ctr macro.
> > > 
> > > Signed-off-by: Quentin Perret <qperret@...gle.com>
> > > ---
> > >  arch/arm64/include/asm/kvm_cpufeature.h |  2 ++
> > >  arch/arm64/kvm/hyp/nvhe/Makefile        |  3 ++-
> > >  arch/arm64/kvm/hyp/nvhe/cache.S         | 13 +++++++++++++
> > >  arch/arm64/kvm/sys_regs.c               |  1 +
> > >  4 files changed, 18 insertions(+), 1 deletion(-)
> > >  create mode 100644 arch/arm64/kvm/hyp/nvhe/cache.S
> > > 
> > > diff --git a/arch/arm64/include/asm/kvm_cpufeature.h b/arch/arm64/include/asm/kvm_cpufeature.h
> > > index 3fd9f60d2180..efba1b89b8a4 100644
> > > --- a/arch/arm64/include/asm/kvm_cpufeature.h
> > > +++ b/arch/arm64/include/asm/kvm_cpufeature.h
> > > @@ -13,3 +13,5 @@
> > >  #define KVM_HYP_CPU_FTR_REG(name) extern struct arm64_ftr_reg kvm_nvhe_sym(name)
> > >  #endif
> > >  #endif
> > > +
> > > +KVM_HYP_CPU_FTR_REG(arm64_ftr_reg_ctrel0);
> > 
> > I still think this is a bit weird. If you really want to macro-ise stuff,
> > then why not follow the sort of thing we do for e.g. per-cpu variables and
> > have separate DECLARE_HYP_CPU_FTR_REG and DEFINE_HYP_CPU_FTR_REG macros.
> > 
> > That way kvm_cpufeature.h can have header guards like a normal header and
> > we can drop the '#ifndef KVM_HYP_CPU_FTR_REG' altogether. I don't think
> > the duplication of the symbol name really matters -- it should fail at
> > build time if something is missing.
> 
> I just tend to hate unnecessary boilerplate, but if you feel strongly
> about it, happy to change :)

I don't like it either, but I prefer it to overriding macros like this! I
think having the "boilerplate" is a better starting point should we decide
to consolidate the definitions somehow.

Will