linux-kernel - Re: [PATCH 4/5] iommu/amd: skip updating the IRTE entry when is

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Date:   Thu, 28 Sep 2023 18:27:57 +0100
From:   Joao Martins <joao.m.martins@...cle.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>, kvm@...r.kernel.org
Cc:     Will Deacon <will@...nel.org>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Paolo Bonzini <pbonzini@...hat.com>, x86@...nel.org,
        Robin Murphy <robin.murphy@....com>, iommu@...ts.linux.dev,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <joro@...tes.org>,
        Sean Christopherson <seanjc@...gle.com>,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] iommu/amd: skip updating the IRTE entry when is_run
 is already false

On 28/09/2023 16:04, Maxim Levitsky wrote:
> When vCPU affinity of an IRTE which already has
> is_run == false, is updated and the update also sets is_run to false,
> there is nothing to do.
> 
> The goal of this patch is to make a call to 'amd_iommu_update_ga()'
> to be relatively cheap if there is nothing to do.
> 
> Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>

Reviewed-by: Joao Martins <joao.m.martins@...cle.com>

> ---
>  drivers/iommu/amd/iommu.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
> index 95bd7c25ba6f366..10bcd436e984672 100644
> --- a/drivers/iommu/amd/iommu.c
> +++ b/drivers/iommu/amd/iommu.c
> @@ -3774,6 +3774,15 @@ int amd_iommu_update_ga(int cpu, bool is_run, void *data)
>  		entry->hi.fields.destination =
>  					APICID_TO_IRTE_DEST_HI(cpu);
>  	}
> +
> +	if (!is_run && !entry->lo.fields_vapic.is_run) {
> +		/*
> +		 * No need to notify the IOMMU about an entry which
> +		 * already has is_run == False
> +		 */
> +		return 0;
> +	}
> +
>  	entry->lo.fields_vapic.is_run = is_run;
>  
>  	return modify_irte_ga(ir_data->iommu, ir_data->irq_2_irte.devid,