Due to a bug in IOVA allocator, page mapping could accidentally overwritten.
We can catch this case by checking 'VALID' bit of GART's page entry prior to
mapping of a page. Since that check introduces a noticeable performance
impact, it should be enabled explicitly by a new CONFIG_TEGRA_IOMMU_GART_DEBUG
option.
Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx>
---
drivers/iommu/Kconfig | 9 +++++++++
drivers/iommu/tegra-gart.c | 16 +++++++++++++++-
2 files changed, 24 insertions(+), 1 deletion(-)
diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
index f3a21343e636..851156a4896d 100644
--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig
@@ -242,6 +242,15 @@ config TEGRA_IOMMU_GART
space through the GART (Graphics Address Relocation Table)
hardware included on Tegra SoCs.
+config TEGRA_IOMMU_GART_DEBUG
+ bool "Debug Tegra GART IOMMU"
+ depends on TEGRA_IOMMU_GART
+ help
+ Properly unmap pages and check whether page is already mapped
+ during of mapping in expense of performance. This allows to
+ catch double page remappings, caused by a bug in the IOVA
+ allocator for example.
+
config TEGRA_IOMMU_SMMU
bool "NVIDIA Tegra SMMU Support"
depends on ARCH_TEGRA
diff --git a/drivers/iommu/tegra-gart.c b/drivers/iommu/tegra-gart.c
index b62f790ad1ba..bc4cb200fa03 100644
--- a/drivers/iommu/tegra-gart.c
+++ b/drivers/iommu/tegra-gart.c
@@ -271,6 +271,7 @@ static int gart_iommu_map(struct iommu_domain *domain, unsigned long iova,
struct gart_device *gart = gart_domain->gart;
unsigned long flags;
unsigned long pfn;
+ unsigned long pte;
if (!gart_iova_range_valid(gart, iova, bytes))
return -EINVAL;
@@ -282,6 +283,14 @@ static int gart_iommu_map(struct iommu_domain *domain, unsigned long iova,
spin_unlock_irqrestore(&gart->pte_lock, flags);
return -EINVAL;
}
+ if (IS_ENABLED(TEGRA_IOMMU_GART_DEBUG)) {
+ pte = gart_read_pte(gart, iova);
+ if (pte & GART_ENTRY_PHYS_ADDR_VALID) {
+ spin_unlock_irqrestore(&gart->pte_lock, flags);
+ dev_err(gart->dev, "Page entry is used already\n");
+ return -EBUSY;
+ }
+ }
gart_set_pte(gart, iova, GART_PTE(pfn));
FLUSH_GART_REGS(gart);
spin_unlock_irqrestore(&gart->pte_lock, flags);
@@ -295,6 +304,10 @@ static size_t gart_iommu_unmap(struct iommu_domain *domain, unsigned long iova,
struct gart_device *gart = gart_domain->gart;
unsigned long flags;
+ /* don't unmap page entries to achieve better performance */
+ if (!IS_ENABLED(TEGRA_IOMMU_GART_DEBUG))
+ return 0;
+
if (!gart_iova_range_valid(gart, iova, bytes))
return 0;
@@ -302,7 +315,8 @@ static size_t gart_iommu_unmap(struct iommu_domain *domain, unsigned long iova,
gart_set_pte(gart, iova, 0);
FLUSH_GART_REGS(gart);
spin_unlock_irqrestore(&gart->pte_lock, flags);
- return 0;
+
+ return bytes;
}
static phys_addr_t gart_iommu_iova_to_phys(struct iommu_domain *domain,
--
2.14.1
--
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