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

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Date:   Fri, 3 Dec 2021 23:45:32 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.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

On Mon, Nov 01, 2021, Vitaly Kuznetsov wrote:
> 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.

Yeah, but the !ex path also uses all_cpus, and in general I'd prefer to keep the
two flush requests bundled together.