linux-kernel - [PATCH 2/3] iommu/vt-d: Allow zero SAGAW if second-stage not supported

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Date:   Wed, 29 Mar 2023 21:47:20 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Joerg Roedel <joro@...tes.org>
Cc:     Kan Liang <kan.liang@...ux.intel.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/3] iommu/vt-d: Allow zero SAGAW if second-stage not supported

The VT-d spec states (in section 11.4.2) that hardware implementations
reporting second-stage translation support (SSTS) field as Clear also
report the SAGAW field as 0. Fix an inappropriate check in alloc_iommu().

Fixes: 792fb43ce2c9 ("iommu/vt-d: Enable Intel IOMMU scalable mode by default")
Suggested-by: Raghunathan Srinivasan <raghunathan.srinivasan@...el.com>
Reviewed-by: Kevin Tian <kevin.tian@...el.com>
Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
Link: https://lore.kernel.org/r/20230318024824.124542-1-baolu.lu@linux.intel.com
---
 drivers/iommu/intel/dmar.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/intel/dmar.c b/drivers/iommu/intel/dmar.c
index 6acfe879589c..23828d189c2a 100644
--- a/drivers/iommu/intel/dmar.c
+++ b/drivers/iommu/intel/dmar.c
@@ -1071,7 +1071,8 @@ static int alloc_iommu(struct dmar_drhd_unit *drhd)
 	}
 
 	err = -EINVAL;
-	if (cap_sagaw(iommu->cap) == 0) {
+	if (!cap_sagaw(iommu->cap) &&
+	    (!ecap_smts(iommu->ecap) || ecap_slts(iommu->ecap))) {
 		pr_info("%s: No supported address widths. Not attempting DMA translation.\n",
 			iommu->name);
 		drhd->ignored = 1;
-- 
2.34.1