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Thu, 16 Jun 2022 00:03:15 +0000 Received: from drhqmail201.nvidia.com (10.126.190.180) by drhqmail202.nvidia.com (10.126.190.181) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.986.22; Wed, 15 Jun 2022 17:03:14 -0700 Received: from Asurada-Nvidia.nvidia.com (10.127.8.11) by mail.nvidia.com (10.126.190.180) with Microsoft SMTP Server id 15.2.986.22 via Frontend Transport; Wed, 15 Jun 2022 17:03:12 -0700 From: Nicolin Chen To: , , , , , , , , , , , , , , CC: , , , , , , , , , , , , , , , , , , , , , , , , , , , Subject: [PATCH v2 2/5] vfio/iommu_type1: Prefer to reuse domains vs match enforced cache coherency Date: Wed, 15 Jun 2022 17:03:01 -0700 Message-ID: <20220616000304.23890-3-nicolinc@nvidia.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20220616000304.23890-1-nicolinc@nvidia.com> References: <20220616000304.23890-1-nicolinc@nvidia.com> MIME-Version: 1.0 X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 983d751c-36ee-48ce-88a5-08da4f2b9ccf X-MS-TrafficTypeDiagnostic: IA1PR12MB6331:EE_ X-Microsoft-Antispam-PRVS: X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 16 Jun 2022 00:03:15.7818 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 983d751c-36ee-48ce-88a5-08da4f2b9ccf X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[12.22.5.238];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: BN8NAM11FT060.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA1PR12MB6331 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org From: Jason Gunthorpe The KVM mechanism for controlling wbinvd is based on OR of the coherency property of all devices attached to a guest, no matter those devices are attached to a single domain or multiple domains. So, there is no value in trying to push a device that could do enforced cache coherency to a dedicated domain vs re-using an existing domain which is non-coherent since KVM won't be able to take advantage of it. This just wastes domain memory. Simplify this code and eliminate the test. This removes the only logic that needed to have a dummy domain attached prior to searching for a matching domain and simplifies the next patches. It's unclear whether we want to further optimize the Intel driver to update the domain coherency after a device is detached from it, at least not before KVM can be verified to handle such dynamics in related emulation paths (wbinvd, vcpu load, write_cr0, ept, etc.). In reality we don't see an usage requiring such optimization as the only device which imposes such non-coherency is Intel GPU which even doesn't support hotplug/hot remove. Signed-off-by: Jason Gunthorpe Signed-off-by: Nicolin Chen Reviewed-by: Kevin Tian --- drivers/vfio/vfio_iommu_type1.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c index c13b9290e357..f4e3b423a453 100644 --- a/drivers/vfio/vfio_iommu_type1.c +++ b/drivers/vfio/vfio_iommu_type1.c @@ -2285,9 +2285,7 @@ static int vfio_iommu_type1_attach_group(void *iommu_data, * testing if they're on the same bus_type. */ list_for_each_entry(d, &iommu->domain_list, next) { - if (d->domain->ops == domain->domain->ops && - d->enforce_cache_coherency == - domain->enforce_cache_coherency) { + if (d->domain->ops == domain->domain->ops) { iommu_detach_group(domain->domain, group->iommu_group); if (!iommu_attach_group(d->domain, group->iommu_group)) {