linux-kernel - Re: [PATCH v2 3/8] KVM: x86: Refactor kvm_hv_flush

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Date:   Mon, 01 Nov 2021 11:00:25 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-hyperv@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, Ajay Garg <ajaygargnsit@...il.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v2 3/8] KVM: x86: Refactor kvm_hv_flush_tlb() to reduce
 indentation

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

> Refactor the "extended" path of kvm_hv_flush_tlb() to reduce the nesting
> depth for the non-fast sparse path, and to make the code more similar to
> the extended path in kvm_hv_send_ipi().
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/hyperv.c | 40 +++++++++++++++++++++-------------------
>  1 file changed, 21 insertions(+), 19 deletions(-)
>
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index cf18aa1712bf..e68931ed27f6 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -1814,31 +1814,33 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc, bool
>  		if (hc->var_cnt != bitmap_weight((unsigned long *)&valid_bank_mask, 64))
>  			return HV_STATUS_INVALID_HYPERCALL_INPUT;
>  
> -		if (!hc->var_cnt && !all_cpus)
> +		if (all_cpus)
> +			goto do_flush;

You could've probably done:

	if (all_cpus) {
		kvm_make_all_cpus_request(kvm, KVM_REQ_TLB_FLUSH_GUEST);
		goto ret_success;
	}

to get rid on the second 'all_cpus' check (and maybe even 'do_flush'
label with some extra work) below.

> +
> +		if (!hc->var_cnt)
>  			goto ret_success;
>  
> -		if (!all_cpus) {
> -			if (hc->fast) {
> -				if (hc->var_cnt > HV_HYPERCALL_MAX_XMM_REGISTERS - 1)
> -					return HV_STATUS_INVALID_HYPERCALL_INPUT;
> -				for (i = 0; i < hc->var_cnt; i += 2) {
> -					sparse_banks[i] = sse128_lo(hc->xmm[i / 2 + 1]);
> -					sparse_banks[i + 1] = sse128_hi(hc->xmm[i / 2 + 1]);
> -				}
> -			} else {
> -				if (hc->var_cnt > 64)
> -					return HV_STATUS_INVALID_HYPERCALL_INPUT;
> -
> -				gpa = hc->ingpa + offsetof(struct hv_tlb_flush_ex,
> -							   hv_vp_set.bank_contents);
> -				if (unlikely(kvm_read_guest(kvm, gpa, sparse_banks,
> -							    hc->var_cnt *
> -							    sizeof(sparse_banks[0]))))
> -					return HV_STATUS_INVALID_HYPERCALL_INPUT;
> +		if (hc->fast) {
> +			if (hc->var_cnt > HV_HYPERCALL_MAX_XMM_REGISTERS - 1)
> +				return HV_STATUS_INVALID_HYPERCALL_INPUT;
> +			for (i = 0; i < hc->var_cnt; i += 2) {
> +				sparse_banks[i] = sse128_lo(hc->xmm[i / 2 + 1]);
> +				sparse_banks[i + 1] = sse128_hi(hc->xmm[i / 2 + 1]);
>  			}
> +			goto do_flush;
>  		}
> +
> +		if (hc->var_cnt > 64)
> +			return HV_STATUS_INVALID_HYPERCALL_INPUT;
> +
> +		gpa = hc->ingpa + offsetof(struct hv_tlb_flush_ex,
> +					   hv_vp_set.bank_contents);
> +		if (unlikely(kvm_read_guest(kvm, gpa, sparse_banks,
> +					    hc->var_cnt * sizeof(sparse_banks[0]))))
> +			return HV_STATUS_INVALID_HYPERCALL_INPUT;
>  	}
>  
> +do_flush:
>  	/*
>  	 * vcpu->arch.cr3 may not be up-to-date for running vCPUs so we can't
>  	 * analyze it here, flush TLB regardless of the specified address space.

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

-- 
Vitaly