linux-kernel - Re: [PATCH v7 01/12] KVM: Rename kvm_arch_flush_remote_tlb() to kvm_arch_flush_remote

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Date:   Wed, 02 Aug 2023 16:54:10 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Raghavendra Rao Ananta <rananta@...gle.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Oliver Upton <oliver.upton@...ux.dev>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Huacai Chen <chenhuacai@...nel.org>,
        Zenghui Yu <yuzenghui@...wei.com>,
        Anup Patel <anup@...infault.org>,
        Atish Patra <atishp@...shpatra.org>,
        Jing Zhang <jingzhangos@...gle.com>,
        Reiji Watanabe <reijiw@...gle.com>,
        Colton Lewis <coltonlewis@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
        linux-mips@...r.kernel.org, kvm-riscv@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, Gavin Shan <gshan@...hat.com>,
        Philippe Mathieu-Daudé <philmd@...aro.org>,
        Shaoqin Huang <shahuang@...hat.com>
Subject: Re: [PATCH v7 01/12] KVM: Rename kvm_arch_flush_remote_tlb() to kvm_arch_flush_remote_tlbs()

On Tue, 01 Aug 2023 01:42:54 +0100,
Raghavendra Rao Ananta <rananta@...gle.com> wrote:
> 
> On Mon, Jul 31, 2023 at 2:42 PM Sean Christopherson <seanjc@...gle.com> wrote:
> >
> > On Mon, Jul 31, 2023, Raghavendra Rao Ananta wrote:
> > > On Thu, Jul 27, 2023 at 3:24 AM Marc Zyngier <maz@...nel.org> wrote:
> > > >
> > > > On Sat, 22 Jul 2023 03:22:40 +0100,
> > > > Raghavendra Rao Ananta <rananta@...gle.com> wrote:
> > > > >
> > > > > From: David Matlack <dmatlack@...gle.com>
> > > > >
> > > > > Rename kvm_arch_flush_remote_tlb() and the associated macro
> > > > > __KVM_HAVE_ARCH_FLUSH_REMOTE_TLB to kvm_arch_flush_remote_tlbs() and
> > > > > __KVM_HAVE_ARCH_FLUSH_REMOTE_TLBS respectively.
> > > > >
> > > > > Making the name plural matches kvm_flush_remote_tlbs() and makes it more
> > > > > clear that this function can affect more than one remote TLB.
> > > > >
> > > > > No functional change intended.
> > > > >
> > > > > Signed-off-by: David Matlack <dmatlack@...gle.com>
> > > > > Signed-off-by: Raghavendra Rao Ananta <rananta@...gle.com>
> > > > > Reviewed-by: Gavin Shan <gshan@...hat.com>
> > > > > Reviewed-by: Philippe Mathieu-Daudé <philmd@...aro.org>
> > > > > Reviewed-by: Shaoqin Huang <shahuang@...hat.com>
> > > > > ---
> > > > >  arch/mips/include/asm/kvm_host.h | 4 ++--
> > > > >  arch/mips/kvm/mips.c             | 2 +-
> > > > >  arch/x86/include/asm/kvm_host.h  | 4 ++--
> > > > >  include/linux/kvm_host.h         | 4 ++--
> > > > >  virt/kvm/kvm_main.c              | 2 +-
> > > > >  5 files changed, 8 insertions(+), 8 deletions(-)
> > > > >
> > > > > diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h
> > > > > index 04cedf9f8811..9b0ad8f3bf32 100644
> > > > > --- a/arch/mips/include/asm/kvm_host.h
> > > > > +++ b/arch/mips/include/asm/kvm_host.h
> > > > > @@ -896,7 +896,7 @@ static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {}
> > > > >  static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {}
> > > > >  static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {}
> > > > >
> > > > > -#define __KVM_HAVE_ARCH_FLUSH_REMOTE_TLB
> > > > > -int kvm_arch_flush_remote_tlb(struct kvm *kvm);
> > > > > +#define __KVM_HAVE_ARCH_FLUSH_REMOTE_TLBS
> > > > > +int kvm_arch_flush_remote_tlbs(struct kvm *kvm);
> > > >
> > > > How about making this prototype global? I don't see a point in having
> > > > it per-architecture, specially as you are adding arm64 to that mix in
> > > > the following patch.
> > > >
> > > We can make it global, but I'm not sure what was the intention of the
> > > original author. My guess is that he was following the same style that
> > > we have for some of the other kvm_arch_*() functions
> > > (kvm_arch_free_vm() for example)?
> >
> > Heh, KVM has a *lot* of code that was written with questionable style.  I agree
> > with Marc, I can't think of a single reason not to have the definition in common
> > code.  Declaring the function doesn't preclude a "static inline" implementation,
> > and we could even keep the prototype under an #ifdef, e.g.
> >
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index 9d3ac7720da9..5ac64f933547 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -1484,6 +1484,8 @@ static inline int kvm_arch_flush_remote_tlb(struct kvm *kvm)
> >  {
> >         return -ENOTSUPP;
> >  }
> > +#else
> > +int kvm_arch_flush_remote_tlb(struct kvm *kvm);
> >  #endif
> >
> >  #ifdef __KVM_HAVE_ARCH_NONCOHERENT_DMA
> >
> Thanks for the suggestions; I can go with a common declaration. Along
> with that, do we want to keep defining
> __KVM_HAVE_ARCH_FLUSH_REMOTE_TLBS in the arch code that supports it or
> convert it into a CONFIG_?

This isn't something that a user can select, more something that is an
architectural decision. Maybe in a later patch if there is a consensus
around that, but probably not as part of this series.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.