linux-kernel - [PATCH 2/2] iommu/vt-d: Avoid unnecessary global DMA cache invalidation

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Message-Id: <20220919062523.3438951-3-baolu.lu@linux.intel.com>
Date:   Mon, 19 Sep 2022 14:25:23 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     iommu@...ts.linux.dev
Cc:     Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Kevin Tian <kevin.tian@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        linux-kernel@...r.kernel.org, Lu Baolu <baolu.lu@...ux.intel.com>
Subject: [PATCH 2/2] iommu/vt-d: Avoid unnecessary global DMA cache invalidation

Some VT-d hardware implementations invalidate all DMA remapping hardware
translation caches as part of SRTP flow. The VT-d spec adds a ESRTPS
(Enhanced Set Root Table Pointer Support, section 11.4.2 in VT-d spec)
capability bit to indicate this. With this bit set, software has no need
to issue the global invalidation request.

Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
---
 drivers/iommu/intel/iommu.h | 1 +
 drivers/iommu/intel/iommu.c | 7 +++++++
 2 files changed, 8 insertions(+)

diff --git a/drivers/iommu/intel/iommu.h b/drivers/iommu/intel/iommu.h
index 5407d82df4d1..251a609fdce3 100644
--- a/drivers/iommu/intel/iommu.h
+++ b/drivers/iommu/intel/iommu.h
@@ -146,6 +146,7 @@
 /*
  * Decoding Capability Register
  */
+#define cap_esrtps(c)		(((c) >> 63) & 1)
 #define cap_esirtps(c)		(((c) >> 62) & 1)
 #define cap_fl5lp_support(c)	(((c) >> 60) & 1)
 #define cap_pi_support(c)	(((c) >> 59) & 1)
diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 8e5d99197d39..c20f3e060bac 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -1239,6 +1239,13 @@ static void iommu_set_root_entry(struct intel_iommu *iommu)
 
 	raw_spin_unlock_irqrestore(&iommu->register_lock, flag);
 
+	/*
+	 * Hardware invalidates all DMA remapping hardware translation
+	 * caches as part of SRTP flow.
+	 */
+	if (cap_esrtps(iommu->cap))
+		return;
+
 	iommu->flush.flush_context(iommu, 0, 0, 0, DMA_CCMD_GLOBAL_INVL);
 	if (sm_supported(iommu))
 		qi_flush_pasid_cache(iommu, 0, QI_PC_GLOBAL, 0);
-- 
2.34.1