[PATCH 1/1] iommu/vt-d: Correctly calculate sagaw value of IOMMU

[PATCH 1/1] iommu/vt-d: Correctly calculate sagaw value of IOMMU

[Lu Baolu]

The Intel IOMMU driver possibly selects between the first-level and the
second-level translation tables for DMA address translation. However,
the levels of page-table walks for the 4KB base page size are calculated
from the SAGAW field of the capability register, which is only valid for
the second-level page table. This causes the IOMMU driver to stop working
if the hardware (or the emulated IOMMU) advertises only first-level
translation capability and reports the SAGAW field as 0.

This solves the above problem by considering both the first level and the
second level when calculating the supported page table levels.

Fixes: b802d070a52a1 ("iommu/vt-d: Use iova over first level")
Cc: stable@vger.kernel.org
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
---
 drivers/iommu/intel/iommu.c | 28 +++++++++++++++++++++++++---
 1 file changed, 25 insertions(+), 3 deletions(-)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 889ad2c9a7b9..2d0d2ef820d2 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -370,14 +370,36 @@ static inline int domain_pfn_supported(struct dmar_domain *domain,
 	return !(addr_width < BITS_PER_LONG && pfn >> addr_width);
 }
 
+/*
+ * Calculate the Supported Adjusted Guest Address Widths of an IOMMU.
+ * Refer to 11.4.2 of the VT-d spec for the encoding of each bit of
+ * the returned SAGAW.
+ */
+static unsigned long __iommu_calculate_sagaw(struct intel_iommu *iommu)
+{
+	unsigned long fl_sagaw, sl_sagaw;
+
+	fl_sagaw = 0x6 | (cap_fl1gp_support(iommu->cap) ? BIT(3) : 0);
+	sl_sagaw = cap_sagaw(iommu->cap);
+
+	/* Second level only. */
+	if (!sm_supported(iommu) || !ecap_flts(iommu->ecap))
+		return sl_sagaw;
+
+	/* First level only. */
+	if (!ecap_slts(iommu->ecap))
+		return fl_sagaw;
+
+	return fl_sagaw & sl_sagaw;
+}
+
 static int __iommu_calculate_agaw(struct intel_iommu *iommu, int max_gaw)
 {
 	unsigned long sagaw;
 	int agaw;
 
-	sagaw = cap_sagaw(iommu->cap);
-	for (agaw = width_to_agaw(max_gaw);
-	     agaw >= 0; agaw--) {
+	sagaw = __iommu_calculate_sagaw(iommu);
+	for (agaw = width_to_agaw(max_gaw); agaw >= 0; agaw--) {
 		if (test_bit(agaw, &sagaw))
 			break;
 	}
-- 
2.25.1

Re: [PATCH 1/1] iommu/vt-d: Correctly calculate sagaw value of IOMMU

[Baolu Lu]

On 2022/8/17 10:35, Lu Baolu wrote:
> The Intel IOMMU driver possibly selects between the first-level and the
> second-level translation tables for DMA address translation. However,
> the levels of page-table walks for the 4KB base page size are calculated
> from the SAGAW field of the capability register, which is only valid for
> the second-level page table. This causes the IOMMU driver to stop working
> if the hardware (or the emulated IOMMU) advertises only first-level
> translation capability and reports the SAGAW field as 0.
> 
> This solves the above problem by considering both the first level and the
> second level when calculating the supported page table levels.
> 
> Fixes: b802d070a52a1 ("iommu/vt-d: Use iova over first level")
> Cc:stable@vger.kernel.org
> Signed-off-by: Lu Baolu<baolu.lu@linux.intel.com>

This patch has been queued:

https://lore.kernel.org/linux-iommu/20220823061557.1631056-1-baolu.lu@linux.intel.com/

Best regards,
baolu