linux-kernel - Re: [PATCH 1/2] KVM: VMX: Assert that IRQs are disabled when putting vCPU on PI wakeup list

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Message-ID: <7ddba836af37493764c56098a46aad7ee202b6ba.camel@redhat.com>
Date: Tue, 01 Apr 2025 15:04:24 -0400
From: Maxim Levitsky <mlevitsk@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini
 <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, Yan Zhao
	 <yan.y.zhao@...el.com>
Subject: Re: [PATCH 1/2] KVM: VMX: Assert that IRQs are disabled when
 putting vCPU on PI wakeup list

On Tue, 2025-04-01 at 08:47 -0700, Sean Christopherson wrote:
> Assert that IRQs are already disabled when putting a vCPU on a CPU's PI
> wakeup list, as opposed to saving/disabling+restoring IRQs.  KVM relies on
> IRQs being disabled until the vCPU task is fully scheduled out, i.e. until
> the scheduler has dropped all of its per-CPU locks (e.g. for the runqueue),
> as attempting to wake the task while it's being scheduled out could lead
> to deadlock.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/vmx/posted_intr.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/posted_intr.c b/arch/x86/kvm/vmx/posted_intr.c
> index ec08fa3caf43..840d435229a8 100644
> --- a/arch/x86/kvm/vmx/posted_intr.c
> +++ b/arch/x86/kvm/vmx/posted_intr.c
> @@ -148,9 +148,8 @@ static void pi_enable_wakeup_handler(struct kvm_vcpu *vcpu)
>  	struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);
>  	struct vcpu_vmx *vmx = to_vmx(vcpu);
>  	struct pi_desc old, new;
> -	unsigned long flags;
>  
> -	local_irq_save(flags);
> +	lockdep_assert_irqs_disabled();
>  
>  	raw_spin_lock(&per_cpu(wakeup_vcpus_on_cpu_lock, vcpu->cpu));
>  	list_add_tail(&vmx->pi_wakeup_list,
> @@ -176,8 +175,6 @@ static void pi_enable_wakeup_handler(struct kvm_vcpu *vcpu)
>  	 */
>  	if (pi_test_on(&new))
>  		__apic_send_IPI_self(POSTED_INTR_WAKEUP_VECTOR);
> -
> -	local_irq_restore(flags);
>  }
>  
>  static bool vmx_needs_pi_wakeup(struct kvm_vcpu *vcpu)


Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>

Best regards,
	Maxim Levitsky