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Message-ID: <Y4kvYlCbhj87rceF@google.com>
Date: Thu, 1 Dec 2022 22:49:06 +0000
From: Sean Christopherson <seanjc@...gle.com>
To: Philippe Mathieu-Daudé <philmd@...aro.org>
Cc: Paolo Bonzini <pbonzini@...hat.com>, Marc Zyngier <maz@...nel.org>,
Huacai Chen <chenhuacai@...nel.org>,
Aleksandar Markovic <aleksandar.qemu.devel@...il.com>,
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Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>,
Christian Borntraeger <borntraeger@...ux.ibm.com>,
Janosch Frank <frankja@...ux.ibm.com>,
Claudio Imbrenda <imbrenda@...ux.ibm.com>,
Matthew Rosato <mjrosato@...ux.ibm.com>,
Eric Farman <farman@...ux.ibm.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
David Woodhouse <dwmw2@...radead.org>,
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Alexandru Elisei <alexandru.elisei@....com>,
Suzuki K Poulose <suzuki.poulose@....com>,
Oliver Upton <oliver.upton@...ux.dev>,
Atish Patra <atishp@...shpatra.org>,
David Hildenbrand <david@...hat.com>, kvm@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
kvmarm@...ts.cs.columbia.edu, linux-mips@...r.kernel.org,
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Kai Huang <kai.huang@...el.com>, Chao Gao <chao.gao@...el.com>,
Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2 21/50] KVM: MIPS: Hardcode callbacks to hardware
virtualization extensions
On Thu, Dec 01, 2022, Philippe Mathieu-Daudé wrote:
> On 1/12/22 00:09, Sean Christopherson wrote:
> > Now that KVM no longer supports trap-and-emulate (see commit 45c7e8af4a5e
> > "MIPS: Remove KVM_TE support"), hardcode the MIPS callbacks to the
> > virtualization callbacks.
> >
> > Harcoding the callbacks eliminates the technically-unnecessary check on
> > non-NULL kvm_mips_callbacks in kvm_arch_init(). MIPS has never supported
> > multiple in-tree modules, i.e. barring an out-of-tree module, where
> > copying and renaming kvm.ko counts as "out-of-tree", KVM could never
> > encounter a non-NULL set of callbacks during module init.
> >
> > The callback check is also subtly broken, as it is not thread safe,
> > i.e. if there were multiple modules, loading both concurrently would
> > create a race between checking and setting kvm_mips_callbacks.
> >
> > Given that out-of-tree shenanigans are not the kernel's responsibility,
> > hardcode the callbacks to simplify the code.
> >
> > Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> > ---
> > arch/mips/include/asm/kvm_host.h | 2 +-
> > arch/mips/kvm/Makefile | 2 +-
> > arch/mips/kvm/callback.c | 14 --------------
> > arch/mips/kvm/mips.c | 9 ++-------
> > arch/mips/kvm/vz.c | 7 ++++---
> > 5 files changed, 8 insertions(+), 26 deletions(-)
> > delete mode 100644 arch/mips/kvm/callback.c
> >
> > diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h
> > index 28f0ba97db71..2803c9c21ef9 100644
> > --- a/arch/mips/include/asm/kvm_host.h
> > +++ b/arch/mips/include/asm/kvm_host.h
> > @@ -758,7 +758,7 @@ struct kvm_mips_callbacks {
> > void (*vcpu_reenter)(struct kvm_vcpu *vcpu);
> > };
> > extern struct kvm_mips_callbacks *kvm_mips_callbacks;
>
> IIUC we could even constify this pointer.
Good point. Protecting the pointer itself is a bit gross, but it is a nice
stopgap until the callbacks are gone. I'll fold this in. Thanks!
extern const struct kvm_mips_callbacks * const kvm_mips_callbacks;
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