linux-kernel - Re: [PATCH 1/4] KVM: x86: hyper-v: Drop redundant 'ex' parameter from kvm_hv_send

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Message-ID: <87y21vcnxy.fsf@redhat.com>
Date:   Mon, 28 Feb 2022 10:58:33 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>, kvm@...r.kernel.org
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Siddharth Chandrasekaran <sidcha@...zon.de>,
        linux-kernel@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH 1/4] KVM: x86: hyper-v: Drop redundant 'ex' parameter
 from kvm_hv_send_ipi()

Maxim Levitsky <mlevitsk@...hat.com> writes:

> On Tue, 2022-02-22 at 16:46 +0100, Vitaly Kuznetsov wrote:
>> 'struct kvm_hv_hcall' has all the required information already,
>> there's no need to pass 'ex' additionally.
>> 
>> No functional change intended.
>> 
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
>> ---
>>  arch/x86/kvm/hyperv.c | 8 ++++----
>>  1 file changed, 4 insertions(+), 4 deletions(-)
>> 
>> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
>> index 6e38a7d22e97..15b6a7bd2346 100644
>> --- a/arch/x86/kvm/hyperv.c
>> +++ b/arch/x86/kvm/hyperv.c
>> @@ -1875,7 +1875,7 @@ static void kvm_send_ipi_to_many(struct kvm *kvm, u32 vector,
>>  	}
>>  }
>>  
>> -static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc, bool ex)
>> +static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
>>  {
>>  	struct kvm *kvm = vcpu->kvm;
>>  	struct hv_send_ipi_ex send_ipi_ex;
>> @@ -1889,7 +1889,7 @@ static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc, bool
>>  	u32 vector;
>>  	bool all_cpus;
>>  
>> -	if (!ex) {
>> +	if (hc->code == HVCALL_SEND_IPI) {
>
> I am thinking, if we already touch this code,
> why not to use switch here instead on the hc->code,
> so that we can catch this function being called with something else than
> HVCALL_SEND_IPI_EX

I'm not against this second line of defense but kvm_hv_send_ipi() is
only called explicitly from kvm_hv_hypercall()'s switch so something is
really screwed up if we end up seeing something different from
HVCALL_SEND_IPI_EX/HVCALL_SEND_IPI here.

I'm now working on a bigger series for TLB flush improvements, will use
your suggestion there, thanks!

>
>>  		if (!hc->fast) {
>>  			if (unlikely(kvm_read_guest(kvm, hc->ingpa, &send_ipi,
>>  						    sizeof(send_ipi))))
>> @@ -2279,14 +2279,14 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
>>  			ret = HV_STATUS_INVALID_HYPERCALL_INPUT;
>>  			break;
>>  		}
>> -		ret = kvm_hv_send_ipi(vcpu, &hc, false);
>> +		ret = kvm_hv_send_ipi(vcpu, &hc);
>>  		break;
>>  	case HVCALL_SEND_IPI_EX:
>>  		if (unlikely(hc.fast || hc.rep)) {
>>  			ret = HV_STATUS_INVALID_HYPERCALL_INPUT;
>>  			break;
>>  		}
>> -		ret = kvm_hv_send_ipi(vcpu, &hc, true);
>> +		ret = kvm_hv_send_ipi(vcpu, &hc);
>>  		break;
>>  	case HVCALL_POST_DEBUG_DATA:
>>  	case HVCALL_RETRIEVE_DEBUG_DATA:
>
>
>
> Other than this minor nitpick:
>
> Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
>
>
> Best regards,
> 	Maxim Levitsky
>

-- 
Vitaly