Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Sender: Paolo Bonzini <paolo.bonzini@gmail.com>
Message-ID: <78616cf8-2693-72cc-c2cc-5a849116ffc7@redhat.com>
Date:   Wed, 17 Aug 2022 17:31:27 +0200
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.12.0
Subject: Re: [PATCH v2 2/9] KVM: x86: remove return value of kvm_vcpu_block
Content-Language: en-US
To:     Sean Christopherson <seanjc@google.com>
Cc:     linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        mlevitsk@redhat.com, vkuznets@redhat.com
References: <20220811210605.402337-1-pbonzini@redhat.com>
 <20220811210605.402337-3-pbonzini@redhat.com> <Yvwpb6ofD1S+Rqk1@google.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
In-Reply-To: <Yvwpb6ofD1S+Rqk1@google.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 8/17/22 01:34, Sean Christopherson wrote:
> Isn't freeing up the return from kvm_vcpu_check_block() unnecessary?  Can't we
> just do:
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 9f11b505cbee..ccb9f8bdeb18 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -10633,7 +10633,7 @@ static inline int vcpu_block(struct kvm_vcpu *vcpu)
>                  if (hv_timer)
>                          kvm_lapic_switch_to_hv_timer(vcpu);
> 
> -               if (!kvm_check_request(KVM_REQ_UNHALT, vcpu))
> +               if (!kvm_arch_vcpu_runnable(vcpu))
>                          return 1;
>          }
> 
> 
> which IMO is more intuitive and doesn't require reworking halt-polling (again).

This was my first idea indeed.  However I didn't like calling 
kvm_arch_vcpu_runnable() again and "did it schedule()" seemed to be a 
less interesting result from kvm_vcpu_block() (and in fact 
kvm_vcpu_halt() does not bother passing it up the return chain).

Paolo