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Date:   Mon, 5 Dec 2022 21:12:39 +0000
From:   Sean Christopherson <seanjc@google.com>
To:     Isaku Yamahata <isaku.yamahata@gmail.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>, Marc Zyngier <maz@kernel.org>,
        Huacai Chen <chenhuacai@kernel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>,
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        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        Janosch Frank <frankja@linux.ibm.com>,
        Claudio Imbrenda <imbrenda@linux.ibm.com>,
        Matthew Rosato <mjrosato@linux.ibm.com>,
        Eric Farman <farman@linux.ibm.com>,
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        David Woodhouse <dwmw2@infradead.org>,
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        Alexandru Elisei <alexandru.elisei@arm.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
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        David Hildenbrand <david@redhat.com>, kvm@vger.kernel.org,
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        linux-kernel@vger.kernel.org, Yuan Yao <yuan.yao@intel.com>,
        Cornelia Huck <cohuck@redhat.com>,
        Isaku Yamahata <isaku.yamahata@intel.com>,
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        Fabiano Rosas <farosas@linux.ibm.com>,
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        Kai Huang <kai.huang@intel.com>, Chao Gao <chao.gao@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH v2 31/50] KVM: x86: Do CPU compatibility checks in x86
 code
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References: <20221130230934.1014142-1-seanjc@google.com>
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 <20221205205246.GA3630770@ls.amr.corp.intel.com>
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On Mon, Dec 05, 2022, Isaku Yamahata wrote:
> On Wed, Nov 30, 2022 at 11:09:15PM +0000,
> > index 66f16458aa97..3571bc968cf8 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -9277,10 +9277,36 @@ static inline void kvm_ops_update(struct kvm_x86_init_ops *ops)
> >  	kvm_pmu_ops_update(ops->pmu_ops);
> >  }
> >  
> > +struct kvm_cpu_compat_check {
> > +	struct kvm_x86_init_ops *ops;
> > +	int *ret;
> 
> minor nitpick: just int ret. I don't see the necessity of the pointer.
> Anyway overall it looks good to me.

...

> > @@ -9360,6 +9386,14 @@ static int __kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
> >  	if (r != 0)
> >  		goto out_mmu_exit;
> >  
> > +	c.ret = &r;
> > +	c.ops = ops;
> > +	for_each_online_cpu(cpu) {
> > +		smp_call_function_single(cpu, kvm_x86_check_cpu_compat, &c, 1);
> > +		if (r < 0)
> 
> Here it can be "c.ret < 0".

No, because the below goto leads to "return r", i.e. "c.ret" needs to be propagated
to "r".  That's why the code does the admittedly funky "int *ret" thing.

FWIW, this gets cleanup in the end.  "struct kvm_cpu_compat_check" goes away and
"&r" is passed directly to kvm_x86_check_cpu_compat.

> > +			goto out_hardware_unsetup;