linux-kernel - Re: [PATCH 1/2] KVM: x86: Query vcpu->vcpu

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Date:   Mon, 13 Sep 2021 09:02:46 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] KVM: x86: Query vcpu->vcpu_idx directly and drop
 its accessor

Sean Christopherson <seanjc@...gle.com> writes:

> Read vcpu->vcpu_idx directly instead of bouncing through the one-line
> wrapper, kvm_vcpu_get_idx(), and drop the wrapper.  The wrapper is a
> remnant of the original implementation and serves no purpose; remove it
> before it gains more users.
>
> Back when kvm_vcpu_get_idx() was added by commit 497d72d80a78 ("KVM: Add
> kvm_vcpu_get_idx to get vcpu index in kvm->vcpus"), the implementation
> was more than just a simple wrapper as vcpu->vcpu_idx did not exist and
> retrieving the index meant walking over the vCPU array to find the given
> vCPU.
>
> When vcpu_idx was introduced by commit 8750e72a79dd ("KVM: remember
> position in kvm->vcpus array"), the helper was left behind, likely to
> avoid extra thrash (but even then there were only two users, the original
> arm usage having been removed at some point in the past).
>
> No functional change intended.
>
> Suggested-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/hyperv.c    | 7 +++----
>  arch/x86/kvm/hyperv.h    | 2 +-
>  include/linux/kvm_host.h | 5 -----
>  3 files changed, 4 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index fe4a02715266..04dbc001f4fc 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -939,7 +939,7 @@ static int kvm_hv_vcpu_init(struct kvm_vcpu *vcpu)
>  	for (i = 0; i < ARRAY_SIZE(hv_vcpu->stimer); i++)
>  		stimer_init(&hv_vcpu->stimer[i], i);
>  
> -	hv_vcpu->vp_index = kvm_vcpu_get_idx(vcpu);
> +	hv_vcpu->vp_index = vcpu->vcpu_idx;
>  
>  	return 0;
>  }
> @@ -1444,7 +1444,6 @@ static int kvm_hv_set_msr(struct kvm_vcpu *vcpu, u32 msr, u64 data, bool host)
>  	switch (msr) {
>  	case HV_X64_MSR_VP_INDEX: {
>  		struct kvm_hv *hv = to_kvm_hv(vcpu->kvm);
> -		int vcpu_idx = kvm_vcpu_get_idx(vcpu);
>  		u32 new_vp_index = (u32)data;
>  
>  		if (!host || new_vp_index >= KVM_MAX_VCPUS)
> @@ -1459,9 +1458,9 @@ static int kvm_hv_set_msr(struct kvm_vcpu *vcpu, u32 msr, u64 data, bool host)
>  		 * VP index is changing, adjust num_mismatched_vp_indexes if
>  		 * it now matches or no longer matches vcpu_idx.
>  		 */
> -		if (hv_vcpu->vp_index == vcpu_idx)
> +		if (hv_vcpu->vp_index == vcpu->vcpu_idx)
>  			atomic_inc(&hv->num_mismatched_vp_indexes);
> -		else if (new_vp_index == vcpu_idx)
> +		else if (new_vp_index == vcpu->vcpu_idx)
>  			atomic_dec(&hv->num_mismatched_vp_indexes);
>  
>  		hv_vcpu->vp_index = new_vp_index;
> diff --git a/arch/x86/kvm/hyperv.h b/arch/x86/kvm/hyperv.h
> index 730da8537d05..ed1c4e546d04 100644
> --- a/arch/x86/kvm/hyperv.h
> +++ b/arch/x86/kvm/hyperv.h
> @@ -83,7 +83,7 @@ static inline u32 kvm_hv_get_vpindex(struct kvm_vcpu *vcpu)
>  {
>  	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
>  
> -	return hv_vcpu ? hv_vcpu->vp_index : kvm_vcpu_get_idx(vcpu);
> +	return hv_vcpu ? hv_vcpu->vp_index : vcpu->vcpu_idx;
>  }
>  
>  int kvm_hv_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data, bool host);
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index e4d712e9f760..31071ad821e2 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -721,11 +721,6 @@ static inline struct kvm_vcpu *kvm_get_vcpu_by_id(struct kvm *kvm, int id)
>  	return NULL;
>  }
>  
> -static inline int kvm_vcpu_get_idx(struct kvm_vcpu *vcpu)
> -{
> -	return vcpu->vcpu_idx;
> -}
> -
>  #define kvm_for_each_memslot(memslot, slots)				\
>  	for (memslot = &slots->memslots[0];				\
>  	     memslot < slots->memslots + slots->used_slots; memslot++)	\

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

-- 
Vitaly