linux-kernel - Re: [PATCH v2 30/45] KVM: Move vcpu alloc and init invocation to common code

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Date:   Sat, 25 Jan 2020 19:02:26 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Marc Zyngier <maz@...nel.org>, James Hogan <jhogan@...nel.org>,
        Paul Mackerras <paulus@...abs.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-mips@...r.kernel.org, kvm-ppc@...r.kernel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Greg Kurz <groug@...d.org>
Subject: Re: [PATCH v2 30/45] KVM: Move vcpu alloc and init invocation to
 common code

On Wed, Dec 18, 2019 at 01:55:15PM -0800, Sean Christopherson wrote:
> Now that all architectures tightly couple vcpu allocation/free with the
> mandatory calls to kvm_{un}init_vcpu(), move the sequences verbatim to
> common KVM code.
> 
> Move both allocation and initialization in a single patch to eliminate
> thrash in arch specific code.  The bisection benefits of moving the two
> pieces in separate patches is marginal at best, whereas the odds of
> introducing a transient arch specific bug are non-zero.
> 
> Acked-by: Christoffer Dall <christoffer.dall@....com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> Reviewed-by: Cornelia Huck <cohuck@...hat.com>

[ ... ]

> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 8543d338a06a..2ed76584ebd9 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
>  

[ ... ]

> -struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm,
> -				      unsigned int id)
                                      ^^^^^^^^^^^^^^^
> +int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
>  {
> -	struct kvm_vcpu *vcpu;
>  	struct sie_page *sie_page;
>  	int rc;
>  
> -	rc = -ENOMEM;
> -
> -	vcpu = kmem_cache_zalloc(kvm_vcpu_cache, GFP_KERNEL);
> -	if (!vcpu)
> -		goto out;
> -
> -	rc = kvm_vcpu_init(vcpu, kvm, id);
> -	if (rc)
> -		goto out_free_cpu;
> -
> -	rc = -ENOMEM;
> -
>  	BUILD_BUG_ON(sizeof(struct sie_page) != 4096);
>  	sie_page = (struct sie_page *) get_zeroed_page(GFP_KERNEL);
>  	if (!sie_page)
> -		goto out_uninit_vcpu;
> +		return -ENOMEM;
>  
>  	vcpu->arch.sie_block = &sie_page->sie_block;
>  	vcpu->arch.sie_block->itdba = (unsigned long) &sie_page->itdb;
> @@ -3087,15 +3070,11 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm,
>  		 vcpu->arch.sie_block);
>  	trace_kvm_s390_create_vcpu(id, vcpu, vcpu->arch.sie_block);
                                   ^^^

For extensive changes like this, wouldn't it be desirable to at least
compile test it ?

Guenter