linux-kernel - Re: [PATCH] x86/hyper-v: Stop caring about EOI for direct stimers

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Date:   Wed, 12 Dec 2018 14:09:13 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Roman Kagan <rkagan@...tuozzo.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     "kvm\@vger.kernel.org" <kvm@...r.kernel.org>,
        Radim Krčmář 
        <rkrcmar@...hat.com>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/hyper-v: Stop caring about EOI for direct stimers

Roman Kagan <rkagan@...tuozzo.com> writes:

> [ Sorry, missed this one ]
>
> On Wed, Dec 05, 2018 at 04:36:21PM +0100, Vitaly Kuznetsov wrote:
>> Turns out we over-engineered Direct Mode for stimers a bit: unlike
>> traditional stimers where we may want to try to re-inject the message upon
>> EOI, Direct Mode stimers just set the irq in APIC and kvm_apic_set_irq()
>> fails only when APIC is disabled (see APIC_DM_FIXED case in
>> __apic_accept_irq()). Remove the redundant part.
>> 
>> Suggested-by: Roman Kagan <rkagan@...tuozzo.com>
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
>> ---
>>  arch/x86/kvm/hyperv.c | 36 +++---------------------------------
>>  1 file changed, 3 insertions(+), 33 deletions(-)
>> 
>> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
>> index e6a2a085644a..0a16a77e6ac3 100644
>> --- a/arch/x86/kvm/hyperv.c
>> +++ b/arch/x86/kvm/hyperv.c
>> @@ -56,21 +56,8 @@ static inline int synic_get_sint_vector(u64 sint_value)
>>  static bool synic_has_vector_connected(struct kvm_vcpu_hv_synic *synic,
>>  				      int vector)
>>  {
>> -	struct kvm_vcpu *vcpu = synic_to_vcpu(synic);
>> -	struct kvm_vcpu_hv *hv_vcpu = vcpu_to_hv_vcpu(vcpu);
>> -	struct kvm_vcpu_hv_stimer *stimer;
>>  	int i;
>>  
>> -	for (i = 0; i < ARRAY_SIZE(hv_vcpu->stimer); i++) {
>> -		stimer = &hv_vcpu->stimer[i];
>> -		if (stimer->config.enable && stimer->config.direct_mode &&
>> -		    stimer->config.apic_vector == vector)
>> -			return true;
>> -	}
>> -
>> -	if (vector < HV_SYNIC_FIRST_VALID_VECTOR)
>> -		return false;
>> -
>>  	for (i = 0; i < ARRAY_SIZE(synic->sint); i++) {
>>  		if (synic_get_sint_vector(synic_read_sint(synic, i)) == vector)
>>  			return true;
>> @@ -96,14 +83,14 @@ static bool synic_has_vector_auto_eoi(struct kvm_vcpu_hv_synic *synic,
>>  static void synic_update_vector(struct kvm_vcpu_hv_synic *synic,
>>  				int vector)
>>  {
>> +	if (vector < HV_SYNIC_FIRST_VALID_VECTOR)
>> +		return;
>> +
>>  	if (synic_has_vector_connected(synic, vector))
>>  		__set_bit(vector, synic->vec_bitmap);
>>  	else
>>  		__clear_bit(vector, synic->vec_bitmap);
>>  
>> -	if (vector < HV_SYNIC_FIRST_VALID_VECTOR)
>> -		return;
>> -
>>  	if (synic_has_vector_auto_eoi(synic, vector))
>>  		__set_bit(vector, synic->auto_eoi_bitmap);
>>  	else
>> @@ -382,9 +369,7 @@ int kvm_hv_synic_set_irq(struct kvm *kvm, u32 vpidx, u32 sint)
>>  
>>  void kvm_hv_synic_send_eoi(struct kvm_vcpu *vcpu, int vector)
>>  {
>> -	struct kvm_vcpu_hv *hv_vcpu = vcpu_to_hv_vcpu(vcpu);
>>  	struct kvm_vcpu_hv_synic *synic = vcpu_to_synic(vcpu);
>> -	struct kvm_vcpu_hv_stimer *stimer;
>>  	int i;
>>  
>>  	trace_kvm_hv_synic_send_eoi(vcpu->vcpu_id, vector);
>> @@ -392,14 +377,6 @@ void kvm_hv_synic_send_eoi(struct kvm_vcpu *vcpu, int vector)
>>  	for (i = 0; i < ARRAY_SIZE(synic->sint); i++)
>>  		if (synic_get_sint_vector(synic_read_sint(synic, i)) == vector)
>>  			kvm_hv_notify_acked_sint(vcpu, i);
>> -
>> -	for (i = 0; i < ARRAY_SIZE(hv_vcpu->stimer); i++) {
>> -		stimer = &hv_vcpu->stimer[i];
>> -		if (stimer->msg_pending && stimer->config.enable &&
>> -		    stimer->config.direct_mode &&
>> -		    stimer->config.apic_vector == vector)
>> -			stimer_mark_pending(stimer, false);
>> -	}
>>  }
>>  
>>  static int kvm_hv_set_sint_gsi(struct kvm *kvm, u32 vpidx, u32 sint, int gsi)
>> @@ -566,8 +543,6 @@ static int stimer_start(struct kvm_vcpu_hv_stimer *stimer)
>>  static int stimer_set_config(struct kvm_vcpu_hv_stimer *stimer, u64 config,
>>  			     bool host)
>>  {
>> -	struct kvm_vcpu *vcpu = stimer_to_vcpu(stimer);
>> -	struct kvm_vcpu_hv *hv_vcpu = vcpu_to_hv_vcpu(vcpu);
>>  	union hv_stimer_config new_config = {.as_uint64 = config},
>>  		old_config = {.as_uint64 = stimer->config.as_uint64};
>>  
>> @@ -580,11 +555,6 @@ static int stimer_set_config(struct kvm_vcpu_hv_stimer *stimer, u64 config,
>>  		new_config.enable = 0;
>>  	stimer->config.as_uint64 = new_config.as_uint64;
>>  
>> -	if (old_config.direct_mode)
>> -		synic_update_vector(&hv_vcpu->synic, old_config.apic_vector);
>> -	if (new_config.direct_mode)
>> -		synic_update_vector(&hv_vcpu->synic, new_config.apic_vector);
>> -
>>  	stimer_mark_pending(stimer, false);
>>  	return 0;
>>  }
>
> As discussed in another thread, it seems worth while to make
> stimer_set_config reject vectors 0..15.
>
> Besides I'd rather sqwash this patch into the one that introduced direct
> timers, before it reached Linus' tree.

I'm fine either way, I'm going to send v2 with a new patch adding the
check to stimer_set_config() and leave it up to Paolo if he would want
to squash them all together before sending to Linus.

(Actually I don't see direct stimers in kvm/queue but I think I heard
'queued' from Paolo...)

-- 
Vitaly