linux-kernel - Re: [PATCH v2 38/59] iommu/amd: KVM: SVM: Infer IsRun from validity of pCPU destination

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Message-ID: <9a64d394-e693-49fe-887b-3e4fa0f70878@amd.com>
Date: Fri, 30 May 2025 15:43:26 +0530
From: Sairaj Kodilkar <sarunkod@....com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini
	<pbonzini@...hat.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>, Vasant Hegde <vasant.hegde@....com>, "Maxim
 Levitsky" <mlevitsk@...hat.com>, Joao Martins <joao.m.martins@...cle.com>,
	Francesco Lavra <francescolavra.fl@...il.com>, David Matlack
	<dmatlack@...gle.com>
Subject: Re: [PATCH v2 38/59] iommu/amd: KVM: SVM: Infer IsRun from validity
 of pCPU destination



On 5/23/2025 6:29 AM, Sean Christopherson wrote:
> Infer whether or not a vCPU should be marked running from the validity of
> the pCPU on which it is running.  amd_iommu_update_ga() already skips the
> IRTE update if the pCPU is invalid, i.e. passing %true for is_run with an
> invalid pCPU would be a blatant and egregrious KVM bug.
> 
> Tested-by: Sairaj Kodilkar <sarunkod@....com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>   arch/x86/kvm/svm/avic.c   | 11 +++++------
>   drivers/iommu/amd/iommu.c | 14 +++++++++-----
>   include/linux/amd-iommu.h |  6 ++----
>   3 files changed, 16 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
> index 4747fb09aca4..c79648d96752 100644
> --- a/arch/x86/kvm/svm/avic.c
> +++ b/arch/x86/kvm/svm/avic.c
> @@ -832,7 +832,7 @@ int avic_pi_update_irte(struct kvm_kernel_irqfd *irqfd, struct kvm *kvm,
>   		entry = svm->avic_physical_id_entry;
>   		if (entry & AVIC_PHYSICAL_ID_ENTRY_IS_RUNNING_MASK)
>   			amd_iommu_update_ga(entry & AVIC_PHYSICAL_ID_ENTRY_HOST_PHYSICAL_ID_MASK,
> -					    true, pi_data.ir_data);
> +					    pi_data.ir_data);
>   
>   		irqfd->irq_bypass_data = pi_data.ir_data;
>   		list_add(&irqfd->vcpu_list, &svm->ir_list);
> @@ -841,8 +841,7 @@ int avic_pi_update_irte(struct kvm_kernel_irqfd *irqfd, struct kvm *kvm,
>   	return irq_set_vcpu_affinity(host_irq, NULL);
>   }
>   
> -static inline int
> -avic_update_iommu_vcpu_affinity(struct kvm_vcpu *vcpu, int cpu, bool r)
> +static inline int avic_update_iommu_vcpu_affinity(struct kvm_vcpu *vcpu, int cpu)
>   {

Hi sean

What if define cpu as "unsigned int" instead of "int" and use nr_cpu_ids
as invalid cpu id ? I see that it is common in the other subsystems to
use nr_cpu_ids instead of -1.

Thanks
Sairaj