linux-kernel - Re: [PATCH 25/67] iommu/amd: KVM: SVM: Use pi_desc_addr to derive ga_root

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Message-ID: <d6161236-cba6-40ed-9e8a-010646f6974f@amd.com>
Date: Fri, 18 Apr 2025 17:54:30 +0530
From: Vasant Hegde <vasant.hegde@....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,
 Maxim Levitsky <mlevitsk@...hat.com>,
 Joao Martins <joao.m.martins@...cle.com>, David Matlack <dmatlack@...gle.com>
Subject: Re: [PATCH 25/67] iommu/amd: KVM: SVM: Use pi_desc_addr to derive
 ga_root_ptr

On 4/5/2025 1:08 AM, Sean Christopherson wrote:
> Use vcpu_data.pi_desc_addr instead of amd_iommu_pi_data.base to get the
> GA root pointer.  KVM is the only source of amd_iommu_pi_data.base, and
> KVM's one and only path for writing amd_iommu_pi_data.base computes the
> exact same value for vcpu_data.pi_desc_addr and amd_iommu_pi_data.base,
> and fills amd_iommu_pi_data.base if and only if vcpu_data.pi_desc_addr is
> valid, i.e. amd_iommu_pi_data.base is fully redundant.
> 
> Cc: Maxim Levitsky <mlevitsk@...hat.com>
> Reviewed-by: Joao Martins <joao.m.martins@...cle.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed-by: Vasant Hegde <vasant.hegde@....com>

-Vasant


> ---
>  arch/x86/kvm/svm/avic.c   | 7 +++++--
>  drivers/iommu/amd/iommu.c | 2 +-
>  include/linux/amd-iommu.h | 1 -
>  3 files changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
> index 60e6e82fe41f..9024b9fbca53 100644
> --- a/arch/x86/kvm/svm/avic.c
> +++ b/arch/x86/kvm/svm/avic.c
> @@ -902,8 +902,11 @@ int avic_pi_update_irte(struct kvm_kernel_irqfd *irqfd, struct kvm *kvm,
>  
>  			enable_remapped_mode = false;
>  
> -			/* Try to enable guest_mode in IRTE */
> -			pi.base = avic_get_backing_page_address(svm);
> +			/*
> +			 * Try to enable guest_mode in IRTE.  Note, the address
> +			 * of the vCPU's AVIC backing page is passed to the
> +			 * IOMMU via vcpu_info->pi_desc_addr.
> +			 */
>  			pi.ga_tag = AVIC_GATAG(to_kvm_svm(kvm)->avic_vm_id,
>  						     svm->vcpu.vcpu_id);
>  			pi.is_guest_mode = true;
> diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
> index 4f69a37cf143..635774642b89 100644
> --- a/drivers/iommu/amd/iommu.c
> +++ b/drivers/iommu/amd/iommu.c
> @@ -3860,7 +3860,7 @@ static int amd_ir_set_vcpu_affinity(struct irq_data *data, void *vcpu_info)
>  
>  	pi_data->prev_ga_tag = ir_data->cached_ga_tag;
>  	if (pi_data->is_guest_mode) {
> -		ir_data->ga_root_ptr = (pi_data->base >> 12);
> +		ir_data->ga_root_ptr = (vcpu_pi_info->pi_desc_addr >> 12);
>  		ir_data->ga_vector = vcpu_pi_info->vector;
>  		ir_data->ga_tag = pi_data->ga_tag;
>  		ret = amd_iommu_activate_guest_mode(ir_data);
> diff --git a/include/linux/amd-iommu.h b/include/linux/amd-iommu.h
> index 062fbd4c9b77..4f433ef39188 100644
> --- a/include/linux/amd-iommu.h
> +++ b/include/linux/amd-iommu.h
> @@ -20,7 +20,6 @@ struct amd_iommu;
>  struct amd_iommu_pi_data {
>  	u32 ga_tag;
>  	u32 prev_ga_tag;
> -	u64 base;
>  	bool is_guest_mode;
>  	struct vcpu_data *vcpu_data;
>  	void *ir_data;