linux-kernel - Re: [PATCH 30/67] KVM: VMX: Stop walking list of routing table entries when updating IRTE

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Message-ID: <d270ff32-7763-40d5-a4dc-3970383571dc@redhat.com>
Date: Tue, 8 Apr 2025 19:00:25 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>, Joerg Roedel <joro@...tes.org>,
 David Woodhouse <dwmw2@...radead.org>, Lu Baolu <baolu.lu@...ux.intel.com>
Cc: kvm@...r.kernel.org, iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
 Maxim Levitsky <mlevitsk@...hat.com>,
 Joao Martins <joao.m.martins@...cle.com>, David Matlack <dmatlack@...gle.com>
Subject: Re: [PATCH 30/67] KVM: VMX: Stop walking list of routing table
 entries when updating IRTE

On 4/4/25 21:38, Sean Christopherson wrote:
> Now that KVM provides the to-be-updated routing entry, stop walking the
> routing table to find that entry.  KVM, via setup_routing_entry() and
> sanity checked by kvm_get_msi_route(), disallows having a GSI configured
> to trigger multiple MSIs, i.e. the for-loop can only process one entry.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>   arch/x86/kvm/vmx/posted_intr.c | 100 +++++++++++----------------------
>   1 file changed, 33 insertions(+), 67 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/posted_intr.c b/arch/x86/kvm/vmx/posted_intr.c
> index 00818ca30ee0..786912cee3f8 100644
> --- a/arch/x86/kvm/vmx/posted_intr.c
> +++ b/arch/x86/kvm/vmx/posted_intr.c
> @@ -268,78 +268,44 @@ int vmx_pi_update_irte(struct kvm_kernel_irqfd *irqfd, struct kvm *kvm,
>   		       unsigned int host_irq, uint32_t guest_irq,
>   		       struct kvm_kernel_irq_routing_entry *new)
>   {
> -	struct kvm_kernel_irq_routing_entry *e;
> -	struct kvm_irq_routing_table *irq_rt;
> -	bool enable_remapped_mode = true;
>   	struct kvm_lapic_irq irq;
>   	struct kvm_vcpu *vcpu;
>   	struct vcpu_data vcpu_info;
> -	bool set = !!new;
> -	int idx, ret = 0;
>   
>   	if (!vmx_can_use_vtd_pi(kvm))
>   		return 0;
>   
> -	idx = srcu_read_lock(&kvm->irq_srcu);
> -	irq_rt = srcu_dereference(kvm->irq_routing, &kvm->irq_srcu);
> -	if (guest_irq >= irq_rt->nr_rt_entries ||
> -	    hlist_empty(&irq_rt->map[guest_irq])) {
> -		pr_warn_once("no route for guest_irq %u/%u (broken user space?)\n",
> -			     guest_irq, irq_rt->nr_rt_entries);
> -		goto out;
> -	}
> -
> -	hlist_for_each_entry(e, &irq_rt->map[guest_irq], link) {
> -		if (e->type != KVM_IRQ_ROUTING_MSI)
> -			continue;
> -
> -		WARN_ON_ONCE(new && memcmp(e, new, sizeof(*new)));

Alternatively, if you want to keep patches 28/29 separate, you could add 
this WARN_ON_ONCE to avic.c in the exact same place after checking 
e->type -- not so much for asserting purposes, but more to document 
what's going on for the reviewer.

Paolo