Re: [PATCH v5 8/9] iommu/arm-smmu-v3: Skip cd sync if CD table isn't active
From: Will Deacon <will@kernel.org>
Date: 2023-08-09 13:50:24
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linux-iommu, lkml
On Wed, Aug 09, 2023 at 01:12:04AM +0800, Michael Shavit wrote:
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.
Why is this path worth optimising?
quoted hunk ↗ jump to hunk
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 f5ad386cc8760..488d12dd2d4aa 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;
Doesn't this interact badly with the sync in arm_smmu_detach_dev(), which I think happens after zapping the STE?
quoted hunk ↗ jump to hunk
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. */
Why does this patch need to update this comment? Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel