[PATCH AUTOSEL 5.4 070/130] iommu/tegra-smmu: Expand mutex protection range

Sasha Levin
2020-12-23T02:58:40Z

From: Nicolin Chen <nicoleotsuka@gmail.com>

[ Upstream commit d5f583bf8654c231b781096bc1a186065cda72b3 ]

This is used to protect potential race condition at use_count.
since probes of client drivers, calling attach_dev(), may run
concurrently.

Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
Tested-by: Dmitry Osipenko <digetx@gmail.com>
Reviewed-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Link: https://lore.kernel.org/r/20201125101013.14953-3-nicoleotsuka@gmail.com
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/iommu/tegra-smmu.c | 34 +++++++++++++++++++++-------------
1 file changed, 21 insertions(+), 13 deletions(-)

diff --git a/drivers/iommu/tegra-smmu.c b/drivers/iommu/tegra-smmu.c
index dd486233e2828..41be3e2202971 100644
--- a/drivers/iommu/tegra-smmu.c
+++ b/drivers/iommu/tegra-smmu.c
@@ -247,26 +247,19 @@ static int tegra_smmu_alloc_asid(struct tegra_smmu *smmu, unsigned int *idp)
{
unsigned long id;

- mutex_lock(&smmu->lock);
-
id = find_first_zero_bit(smmu->asids, smmu->soc->num_asids);
- if (id >= smmu->soc->num_asids) {
- mutex_unlock(&smmu->lock);
+ if (id >= smmu->soc->num_asids)
return -ENOSPC;
- }

set_bit(id, smmu->asids);
*idp = id;

- mutex_unlock(&smmu->lock);
return 0;
}

static void tegra_smmu_free_asid(struct tegra_smmu *smmu, unsigned int id)
{
- mutex_lock(&smmu->lock);
clear_bit(id, smmu->asids);
- mutex_unlock(&smmu->lock);
}

static bool tegra_smmu_capable(enum iommu_cap cap)
@@ -404,17 +397,21 @@ static int tegra_smmu_as_prepare(struct tegra_smmu *smmu,
struct tegra_smmu_as *as)
{
u32 value;
- int err;
+ int err = 0;
+
+ mutex_lock(&smmu->lock);

if (as->use_count > 0) {
as->use_count++;
- return 0;
+ goto unlock;
}

as->pd_dma = dma_map_page(smmu->dev, as->pd, 0, SMMU_SIZE_PD,
DMA_TO_DEVICE);
- if (dma_mapping_error(smmu->dev, as->pd_dma))
- return -ENOMEM;
+ if (dma_mapping_error(smmu->dev, as->pd_dma)) {
+ err = -ENOMEM;
+ goto unlock;
+ }

/* We can't handle 64-bit DMA addresses */
if (!smmu_dma_addr_valid(smmu, as->pd_dma)) {
@@ -437,24 +434,35 @@ static int tegra_smmu_as_prepare(struct tegra_smmu *smmu,
as->smmu = smmu;
as->use_count++;

+ mutex_unlock(&smmu->lock);
+
return 0;

err_unmap:
dma_unmap_page(smmu->dev, as->pd_dma, SMMU_SIZE_PD, DMA_TO_DEVICE);
+unlock:
+ mutex_unlock(&smmu->lock);
+
return err;
}

static void tegra_smmu_as_unprepare(struct tegra_smmu *smmu,
struct tegra_smmu_as *as)
{
- if (--as->use_count > 0)
+ mutex_lock(&smmu->lock);
+
+ if (--as->use_count > 0) {
+ mutex_unlock(&smmu->lock);
return;
+ }

tegra_smmu_free_asid(smmu, as->id);

dma_unmap_page(smmu->dev, as->pd_dma, SMMU_SIZE_PD, DMA_TO_DEVICE);

as->smmu = NULL;
+
+ mutex_unlock(&smmu->lock);
}

static int tegra_smmu_attach_dev(struct iommu_domain *domain,
--
2.27.0