[PATCH 6/6] iommu/vt-d: Avoid unnecessary global DMA cache invalidation

From: Lu Baolu
Date: Thu Sep 22 2022 - 20:48:56 EST


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@xxxxxxxxxxxxxxx>
Reviewed-by: Jerry Snitselaar <jsnitsel@xxxxxxxxxx>
Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
Link: https://lore.kernel.org/r/20220919062523.3438951-3-baolu.lu@xxxxxxxxxxxxxxx
---
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 bddf6c69587d..92023dff9513 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 81a449b5cb91..a8b36c3fddf1 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