linux-kernel - Re: [PATCH v2] KVM: x86: Sync the pending Posted-Interrupts

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Date:   Wed, 30 Jan 2019 09:26:04 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Luwei Kang <luwei.kang@...el.com>, rkrcmar@...hat.com,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        x86@...nel.org
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] KVM: x86: Sync the pending Posted-Interrupts

On 30/01/19 01:59, Luwei Kang wrote:
> Some Posted-Interrupts from passthrough devices may be lost or
> overwritten when the vCPU is in runnable state.
> 
> The SN (Suppress Notification) of PID (Posted Interrupt Descriptor) will
> be set when the vCPU is preempted (vCPU in KVM_MP_STATE_RUNNABLE state
> but not running on physical CPU). If a posted interrupt coming at this
> time, the irq remmaping facility will set the bit of PIR (Posted
> Interrupt Requests) without ON (Outstanding Notification).
> So this interrupt can't be sync to APIC virtualization register and
> will not be handled by Guest because ON is zero.
> 
> Signed-off-by: Luwei Kang <luwei.kang@...el.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 2 +-
>  arch/x86/kvm/x86.c     | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index f6915f1..820a03b 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -6048,7 +6048,7 @@ static int vmx_sync_pir_to_irr(struct kvm_vcpu *vcpu)
>  	bool max_irr_updated;
>  
>  	WARN_ON(!vcpu->arch.apicv_active);
> -	if (pi_test_on(&vmx->pi_desc)) {
> +	if (!bitmap_empty((unsigned long *)vmx->pi_desc.pir, NR_VECTORS)) {
>  		pi_clear_on(&vmx->pi_desc);
>  		/*
>  		 * IOMMU can write to PIR.ON, so the barrier matters even on UP.

This is not what I asked.  You should instead do the check after
pi_clear_sn.

Paolo

> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 02c8e09..c31b608 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -7793,7 +7793,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  	 * 1) We should set ->mode before checking ->requests.  Please see
>  	 * the comment in kvm_vcpu_exiting_guest_mode().
>  	 *
> -	 * 2) For APICv, we should set ->mode before checking PIR.ON.  This
> +	 * 2) For APICv, we should set ->mode before checking PID.PIR. This
>  	 * pairs with the memory barrier implicit in pi_test_and_set_on
>  	 * (see vmx_deliver_posted_interrupt).
>  	 *
>