linux-kernel - [PATCH v3 7/8] iommu/arm-smmu-v3: Skip cd sync if CD table isn't active

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Message-ID: <20230802023524.v3.7.Idedc0f496231e2faab3df057219c5e2d937bbfe4@changeid>
Date:   Wed,  2 Aug 2023 02:35:24 +0800
From:   Michael Shavit <mshavit@...gle.com>
To:     iommu@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Cc:     robin.murphy@....com, will@...nel.org, jean-philippe@...aro.org,
        jgg@...dia.com, nicolinc@...dia.com,
        Michael Shavit <mshavit@...gle.com>
Subject: [PATCH v3 7/8] iommu/arm-smmu-v3: Skip cd sync if CD table isn't active

This commit explicitly keeps track of whether a CD table is installed in
an STE so that arm_smmu_sync_cd can skip the sync when unnecessary. This
was previously achieved through the domain->devices list, but we are
moving to a model where arm_smmu_sync_cd directly operates on a master
and the master's CD table instead of a domain.

Signed-off-by: Michael Shavit <mshavit@...gle.com>
Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
---

Changes in v3:
- Flip the cd_table.installed bit back off when table is detached
- re-order the commit later in the series since flipping the installed
  bit to off isn't obvious when the cd_table is still shared by multiple
  masters.

Changes in v2:
- Store field as a bit instead of a bool. Fix comment about STE being
  live before the sync in write_ctx_desc().

 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 8 +++++++-
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h | 2 ++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
index b05963cd4e5b5..94922d4ff7be0 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -985,6 +985,9 @@ static void arm_smmu_sync_cd(struct arm_smmu_master *master,
 		},
 	};
 
+	if (!master->cd_table.installed)
+		return;
+
 	cmds.num = 0;
 	for (i = 0; i < master->num_streams; i++) {
 		cmd.cfgi.sid = master->streams[i].id;
@@ -1091,7 +1094,7 @@ int arm_smmu_write_ctx_desc(struct arm_smmu_master *master, int ssid,
 		cdptr[3] = cpu_to_le64(cd->mair);
 
 		/*
-		 * STE is live, and the SMMU might read dwords of this CD in any
+		 * STE may be live, and the SMMU might read dwords of this CD in any
 		 * order. Ensure that it observes valid values before reading
 		 * V=1.
 		 */
@@ -1360,6 +1363,9 @@ static void arm_smmu_write_strtab_ent(struct arm_smmu_master *master, u32 sid,
 				  cd_table->l1_desc ?
 					  STRTAB_STE_0_S1FMT_64K_L2 :
 					  STRTAB_STE_0_S1FMT_LINEAR);
+		cd_table->installed = true;
+	} else {
+		master->cd_table.installed = false;
 	}
 
 	if (s2_cfg) {
diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
index f2acfcc1af925..0ee3dc7291a15 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
@@ -599,6 +599,8 @@ struct arm_smmu_ctx_desc_cfg {
 	u8				max_cds_bits;
 	/* Whether CD entries in this table have the stall bit set. */
 	u8				stall_enabled:1;
+	/* Whether this CD table is installed in any STE */
+	u8				installed:1;
 };
 
 struct arm_smmu_s2_cfg {
-- 
2.41.0.585.gd2178a4bd4-goog