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

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Message-Id: <20230928150428.199929-5-mlevitsk@redhat.com>
Date:   Thu, 28 Sep 2023 18:04:27 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     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,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH 4/5] iommu/amd: skip updating the IRTE entry when is_run is already false

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>
---
 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,
-- 
2.26.3