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Message-ID: <b12b9b4b-4a2a-4499-8c71-73b8d2338dec@oracle.com>
Date:   Thu, 28 Sep 2023 18:27:57 +0100
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH 4/5] iommu/amd: skip updating the IRTE entry when is_run
 is already false
Content-Language: en-US
To:     Maxim Levitsky <mlevitsk@redhat.com>, kvm@vger.kernel.org
Cc:     Will Deacon <will@kernel.org>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Paolo Bonzini <pbonzini@redhat.com>, x86@kernel.org,
        Robin Murphy <robin.murphy@arm.com>, iommu@lists.linux.dev,
        Ingo Molnar <mingo@redhat.com>, Joerg Roedel <joro@8bytes.org>,
        Sean Christopherson <seanjc@google.com>,
        "H. Peter Anvin" <hpa@zytor.com>, linux-kernel@vger.kernel.org
References: <20230928150428.199929-1-mlevitsk@redhat.com>
 <20230928150428.199929-5-mlevitsk@redhat.com>
From:   Joao Martins <joao.m.martins@oracle.com>
In-Reply-To: <20230928150428.199929-5-mlevitsk@redhat.com>
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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@redhat.com>

Reviewed-by: Joao Martins <joao.m.martins@oracle.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,