Re: [PATCH v1 1/4] iommu/tegra: gart: Add debugging facility

[Thierry Reding]

On Mon, Apr 09, 2018 at 11:07:19PM +0300, Dmitry Osipenko wrote:
> Page mapping could overwritten by an accident (a bug). 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 small performance impact, it should be
> enabled explicitly using new GART's kernel module 'debug' parameter.
> 
> Signed-off-by: Dmitry Osipenko 
> ---
>  drivers/iommu/tegra-gart.c | 13 +
>  1 file changed, 13 insertions(+)

I think this was discussed before, but this really shouldn't be needed
unless the IOVA allocator or GART driver are buggy.

That said, I think this has some usefulness to find such bugs, so:

Acked-by: Thierry Reding 


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Re: [PATCH v1 1/4] iommu/tegra: gart: Add debugging facility

[Thierry Reding]

On Mon, Apr 09, 2018 at 11:07:19PM +0300, Dmitry Osipenko wrote:
> Page mapping could overwritten by an accident (a bug). 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 small performance impact, it should be
> enabled explicitly using new GART's kernel module 'debug' parameter.
> 
> Signed-off-by: Dmitry Osipenko 
> ---
>  drivers/iommu/tegra-gart.c | 13 +
>  1 file changed, 13 insertions(+)

I think this was discussed before, but this really shouldn't be needed
unless the IOVA allocator or GART driver are buggy.

That said, I think this has some usefulness to find such bugs, so:

Acked-by: Thierry Reding 


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Description: PGP signature

[PATCH v1 1/4] iommu/tegra: gart: Add debugging facility

[Dmitry Osipenko]

Page mapping could overwritten by an accident (a bug). 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 small performance impact, it should be
enabled explicitly using new GART's kernel module 'debug' parameter.

Signed-off-by: Dmitry Osipenko 
---
 drivers/iommu/tegra-gart.c | 13 +
 1 file changed, 13 insertions(+)

diff --git a/drivers/iommu/tegra-gart.c b/drivers/iommu/tegra-gart.c
index b62f790ad1ba..4c0abdcd1ad2 100644
--- a/drivers/iommu/tegra-gart.c
+++ b/drivers/iommu/tegra-gart.c
@@ -72,6 +72,8 @@ struct gart_domain {
 
 static struct gart_device *gart_handle; /* unique for a system */
 
+static bool gart_debug;
+
 #define GART_PTE(_pfn) \
(GART_ENTRY_PHYS_ADDR_VALID | ((_pfn) << PAGE_SHIFT))
 
@@ -271,6 +273,7 @@ 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 +285,14 @@ static int gart_iommu_map(struct iommu_domain *domain, 
unsigned long iova,
spin_unlock_irqrestore(>pte_lock, flags);
return -EINVAL;
}
+   if (gart_debug) {
+   pte = gart_read_pte(gart, iova);
+   if (pte & GART_ENTRY_PHYS_ADDR_VALID) {
+   spin_unlock_irqrestore(>pte_lock, flags);
+   dev_err(gart->dev, "Page entry is in-use\n");
+   return -EBUSY;
+   }
+   }
gart_set_pte(gart, iova, GART_PTE(pfn));
FLUSH_GART_REGS(gart);
spin_unlock_irqrestore(>pte_lock, flags);
@@ -515,7 +526,9 @@ static void __exit tegra_gart_exit(void)
 
 subsys_initcall(tegra_gart_init);
 module_exit(tegra_gart_exit);
+module_param(gart_debug, bool, 0644);
 
+MODULE_PARM_DESC(gart_debug, "Enable GART debugging");
 MODULE_DESCRIPTION("IOMMU API for GART in Tegra20");
 MODULE_AUTHOR("Hiroshi DOYU ");
 MODULE_ALIAS("platform:tegra-gart");
-- 
2.16.3

[PATCH v1 1/4] iommu/tegra: gart: Add debugging facility

[Dmitry Osipenko]

Page mapping could overwritten by an accident (a bug). 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 small performance impact, it should be
enabled explicitly using new GART's kernel module 'debug' parameter.

Signed-off-by: Dmitry Osipenko 
---
 drivers/iommu/tegra-gart.c | 13 +
 1 file changed, 13 insertions(+)

diff --git a/drivers/iommu/tegra-gart.c b/drivers/iommu/tegra-gart.c
index b62f790ad1ba..4c0abdcd1ad2 100644
--- a/drivers/iommu/tegra-gart.c
+++ b/drivers/iommu/tegra-gart.c
@@ -72,6 +72,8 @@ struct gart_domain {
 
 static struct gart_device *gart_handle; /* unique for a system */
 
+static bool gart_debug;
+
 #define GART_PTE(_pfn) \
(GART_ENTRY_PHYS_ADDR_VALID | ((_pfn) << PAGE_SHIFT))
 
@@ -271,6 +273,7 @@ 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 +285,14 @@ static int gart_iommu_map(struct iommu_domain *domain, 
unsigned long iova,
spin_unlock_irqrestore(>pte_lock, flags);
return -EINVAL;
}
+   if (gart_debug) {
+   pte = gart_read_pte(gart, iova);
+   if (pte & GART_ENTRY_PHYS_ADDR_VALID) {
+   spin_unlock_irqrestore(>pte_lock, flags);
+   dev_err(gart->dev, "Page entry is in-use\n");
+   return -EBUSY;
+   }
+   }
gart_set_pte(gart, iova, GART_PTE(pfn));
FLUSH_GART_REGS(gart);
spin_unlock_irqrestore(>pte_lock, flags);
@@ -515,7 +526,9 @@ static void __exit tegra_gart_exit(void)
 
 subsys_initcall(tegra_gart_init);
 module_exit(tegra_gart_exit);
+module_param(gart_debug, bool, 0644);
 
+MODULE_PARM_DESC(gart_debug, "Enable GART debugging");
 MODULE_DESCRIPTION("IOMMU API for GART in Tegra20");
 MODULE_AUTHOR("Hiroshi DOYU ");
 MODULE_ALIAS("platform:tegra-gart");
-- 
2.16.3