RE: [PATCH v7 15/17] KVM: Update Posted-Interrupts Descriptor when vCPU is blocked

[Wu, Feng]

First of all, Paolo, thanks a lot for your review on this series, it really means a lot!:)

> -----Original Message-----
> From: linux-kernel-owner@xxxxxxxxxxxxxxx
> [mailto:linux-kernel-owner@xxxxxxxxxxxxxxx] On Behalf Of Paolo Bonzini
> Sent: Friday, September 11, 2015 7:21 PM
> To: Wu, Feng; alex.williamson@xxxxxxxxxx; joro@xxxxxxxxxx;
> mtosatti@xxxxxxxxxx
> Cc: eric.auger@xxxxxxxxxx; kvm@xxxxxxxxxxxxxxx;
> iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v7 15/17] KVM: Update Posted-Interrupts Descriptor when
> vCPU is blocked
> 
> 
> 
> On 25/08/2015 10:50, Feng Wu wrote:
> > This patch updates the Posted-Interrupts Descriptor when vCPU
> > is blocked.
> >
> > pre-block:
> > - Add the vCPU to the blocked per-CPU list
> > - Set 'NV' to POSTED_INTR_WAKEUP_VECTOR
> >
> > post-block:
> > - Remove the vCPU from the per-CPU list
> >
> > Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
> > ---
> >  arch/x86/include/asm/kvm_host.h |   5 ++
> >  arch/x86/kvm/vmx.c              | 151
> ++++++++++++++++++++++++++++++++++++++++
> >  arch/x86/kvm/x86.c              |  55 ++++++++++++---
> >  include/linux/kvm_host.h        |   3 +
> >  virt/kvm/kvm_main.c             |   3 +
> >  5 files changed, 207 insertions(+), 10 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/kvm_host.h
> b/arch/x86/include/asm/kvm_host.h
> > index 22269b4..32af275 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -554,6 +554,8 @@ struct kvm_vcpu_arch {
> >  	 */
> >  	bool write_fault_to_shadow_pgtable;
> >
> > +	bool halted;
> > +
> >  	/* set at EPT violation at this point */
> >  	unsigned long exit_qualification;
> >
> > @@ -868,6 +870,9 @@ struct kvm_x86_ops {
> >
> >  	void (*pi_clear_sn)(struct kvm_vcpu *vcpu);
> >  	void (*pi_set_sn)(struct kvm_vcpu *vcpu);
> > +
> > +	int (*pi_pre_block)(struct kvm_vcpu *vcpu);
> > +	void (*pi_post_block)(struct kvm_vcpu *vcpu);
> 
> Just pre_block/post_block please.  Also, please document the return
> value of pre_block.
> 
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index ef93fdc..fc7f222 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -5869,7 +5869,13 @@ int kvm_vcpu_halt(struct kvm_vcpu *vcpu)
> >  {
> >  	++vcpu->stat.halt_exits;
> >  	if (irqchip_in_kernel(vcpu->kvm)) {
> > -		vcpu->arch.mp_state = KVM_MP_STATE_HALTED;
> > +		/* Handle posted-interrupt when vCPU is to be halted */
> > +		if (!kvm_x86_ops->pi_pre_block ||
> > +		    (kvm_x86_ops->pi_pre_block &&
> 
> No need to test kvm_x86_ops->pi_pre_block again.
> 
> > +		    kvm_x86_ops->pi_pre_block(vcpu) == 0)) {
> > +			vcpu->arch.halted = true;
> > +			vcpu->arch.mp_state = KVM_MP_STATE_HALTED;
> > +		}
> >  		return 1;
> >  	} else {
> >  		vcpu->run->exit_reason = KVM_EXIT_HLT;
> > @@ -6518,6 +6524,21 @@ static int vcpu_enter_guest(struct kvm_vcpu
> *vcpu)
> >  			kvm_vcpu_reload_apic_access_page(vcpu);
> >  	}
> >
> > +	/*
> > +	 * Since posted-interrupts can be set by VT-d HW now, in this
> > +	 * case, KVM_REQ_EVENT is not set. We move the following
> > +	 * operations out of the if statement.
> > +	 */
> 
> Just "KVM_REQ_EVENT is not set when posted interrupts are set by VT-d
> hardware, so we have to update RVI unconditionally", please.
> 
> Could we skip this (in a future patch) if PI.ON=0?

Do you mean only executing the following code when PI.ON == 1?
Maybe we cannot do that, since 'ON' can be cleared by hypervisor
in lots of places.

> 
> > +	if (kvm_lapic_enabled(vcpu)) {
> > +		/*
> > +		 * Update architecture specific hints for APIC
> > +		 * virtual interrupt delivery.
> > +		 */
> > +		if (kvm_x86_ops->hwapic_irr_update)
> > +			kvm_x86_ops->hwapic_irr_update(vcpu,
> > +				kvm_lapic_find_highest_irr(vcpu));
> > +	}
> > +
> >  	if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win) {
> >  		kvm_apic_accept_events(vcpu);
> >  		if (vcpu->arch.mp_state == KVM_MP_STATE_INIT_RECEIVED) {
> > @@ -6534,13 +6555,6 @@ static int vcpu_enter_guest(struct kvm_vcpu
> *vcpu)
> >  			kvm_x86_ops->enable_irq_window(vcpu);
> >
> >  		if (kvm_lapic_enabled(vcpu)) {
> > -			/*
> > -			 * Update architecture specific hints for APIC
> > -			 * virtual interrupt delivery.
> > -			 */
> > -			if (kvm_x86_ops->hwapic_irr_update)
> > -				kvm_x86_ops->hwapic_irr_update(vcpu,
> > -					kvm_lapic_find_highest_irr(vcpu));
> >  			update_cr8_intercept(vcpu);
> >  			kvm_lapic_sync_to_vapic(vcpu);
> >  		}
> > @@ -6711,10 +6725,31 @@ static int vcpu_run(struct kvm_vcpu *vcpu)
> >
> >  	for (;;) {
> >  		if (vcpu->arch.mp_state == KVM_MP_STATE_RUNNABLE &&
> > -		    !vcpu->arch.apf.halted)
> > +		    !vcpu->arch.apf.halted) {
> > +			/*
> > +			 * For some cases, we can get here with
> > +			 * vcpu->arch.halted being true.
> > +			 */
> 
> Which cases?

See the following scenario:
vcpu_run()
{
......

	vcpu_enter_guest() --> VM_EXIT -> kvm_vcpu_halt() --> vcpu->arch.halted = true;

........

	kvm_check_async_pf_completion()
		--> ...... --> kvm_arch_async_page_present(), in which it set
				vcpu->arch.apf.halted to false and vcpu->arch.mp_state
				to KVM_MP_STATE_RUNNABLE, then next time we re-enter
				the for (;;) loop, it will end up vcpu->arch.halted being true
}

Thanks,
Feng

> 
> Paolo
> 
> > +			if (kvm_x86_ops->pi_post_block && vcpu->arch.halted) {
> > +				kvm_x86_ops->pi_post_block(vcpu);
> > +				vcpu->arch.halted = false;
> > +			}
> > +
> >  			r = vcpu_enter_guest(vcpu);
> > -		else
> > +		} else {
> >  			r = vcpu_block(kvm, vcpu);
> > +
> > +			/*
> > +			 * pi_post_block() must be called after
> > +			 * pi_pre_block() which is called in
> > +			 * kvm_vcpu_halt().
> > +			 */
> > +			if (kvm_x86_ops->pi_post_block && vcpu->arch.halted) {
> > +				kvm_x86_ops->pi_post_block(vcpu);
> > +				vcpu->arch.halted = false;
> > +			}
> > +		}
> > +
> >  		if (r <= 0)
> >  			break;
> >
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index f4005dc..6aa69f4 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -233,6 +233,9 @@ struct kvm_vcpu {
> >  	unsigned long requests;
> >  	unsigned long guest_debug;
> >
> > +	int pre_pcpu;
> > +	struct list_head blocked_vcpu_list;
> > +
> >  	struct mutex mutex;
> >  	struct kvm_run *run;
> >
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 8b8a444..191c7eb 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -220,6 +220,9 @@ int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm
> *kvm, unsigned id)
> >  	init_waitqueue_head(&vcpu->wq);
> >  	kvm_async_pf_vcpu_init(vcpu);
> >
> > +	vcpu->pre_pcpu = -1;
> > +	INIT_LIST_HEAD(&vcpu->blocked_vcpu_list);
> > +
> >  	page = alloc_page(GFP_KERNEL | __GFP_ZERO);
> >  	if (!page) {
> >  		r = -ENOMEM;
> >
> --
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