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

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Date:   Mon, 10 Dec 2018 18:39:22 +0000
From:   Roman Kagan <rkagan@...tuozzo.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/hyper-v: Stop caring about EOI for direct stimers

[ 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.

Roman.