linux-kernel - Re: [v3 23/26] KVM: Update Posted-Interrupts Descriptor when vCPU is preempted

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Date:	Mon, 23 Feb 2015 19:21:38 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Feng Wu <feng.wu@...el.com>
Cc:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	x86@...nel.org, gleb@...nel.org, pbonzini@...hat.com,
	dwmw2@...radead.org, joro@...tes.org, alex.williamson@...hat.com,
	jiang.liu@...ux.intel.com, eric.auger@...aro.org,
	linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
	kvm@...r.kernel.org
Subject: Re: [v3 23/26] KVM: Update Posted-Interrupts Descriptor when vCPU is
 preempted

On Fri, Dec 12, 2014 at 11:14:57PM +0800, Feng Wu wrote:
> This patch updates the Posted-Interrupts Descriptor when vCPU
> is preempted.
> 
> sched out:
> - Set 'SN' to suppress furture non-urgent interrupts posted for
> the vCPU.

What wakes the vcpu in the case of a non-urgent interrupt, then?

I wonder how is software suppose to configure the urgent/non-urgent
flag. Can you give examples of (hypothetical) urgent and non-urgent
interrupts.

> sched in:
> - Clear 'SN'
> - Change NDST if vCPU is scheduled to a different CPU
> - Set 'NV' to POSTED_INTR_VECTOR

What about:

POSTED_INTR_VECTOR interrupt handler:
- Wakeup vcpu.
- Set 'SN' to suppress future interrupts.

HLT emulation entry:
- Clear 'SN' to receive VT-d interrupt notification.

> Signed-off-by: Feng Wu <feng.wu@...el.com>
> ---
>  arch/x86/kvm/vmx.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 44 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index ee3b735..bf2e6cd 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -1916,10 +1916,54 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>  		vmcs_writel(HOST_IA32_SYSENTER_ESP, sysenter_esp); /* 22.2.3 */
>  		vmx->loaded_vmcs->cpu = cpu;
>  	}
> +
> +	if (irq_remapping_cap(IRQ_POSTING_CAP)) {
> +		struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);
> +		struct pi_desc old, new;
> +		unsigned int dest;
> +
> +		memset(&old, 0, sizeof(old));
> +		memset(&new, 0, sizeof(new));
> +
> +		do {
> +			old.control = new.control = pi_desc->control;
> +			if (vcpu->cpu != cpu) {
> +				dest = cpu_physical_id(cpu);
> +
> +				if (x2apic_enabled())
> +					new.ndst = dest;
> +				else
> +					new.ndst = (dest << 8) & 0xFF00;
> +			}
> +
> +			pi_clear_sn(&new);
> +
> +			/* set 'NV' to 'notification vector' */
> +			new.nv = POSTED_INTR_VECTOR;
> +		} while (cmpxchg(&pi_desc->control, old.control,
> +				new.control) != old.control);
> +	}
>  }
>  
>  static void vmx_vcpu_put(struct kvm_vcpu *vcpu)
>  {
> +	if (irq_remapping_cap(IRQ_POSTING_CAP)) {
> +		struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);
> +		struct pi_desc old, new;
> +
> +		memset(&old, 0, sizeof(old));
> +		memset(&new, 0, sizeof(new));
> +
> +		/* Set SN when the vCPU is preempted */
> +		if (vcpu->preempted) {
> +			do {
> +				old.control = new.control = pi_desc->control;
> +				pi_set_sn(&new);
> +			} while (cmpxchg(&pi_desc->control, old.control,
> +					new.control) != old.control);
> +		}
> +	}
> +
>  	__vmx_load_host_state(to_vmx(vcpu));
>  	if (!vmm_exclusive) {
>  		__loaded_vmcs_clear(to_vmx(vcpu)->loaded_vmcs);
> -- 
> 1.9.1
> 
> --
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