[PATCH 3.12 047/118] iommu/arm-smmu: use mutex instead of spinlock for locking page tables

Greg Kroah-Hartman
2013-12-18T21:39:07Z

From: Will Deacon <will.deacon@arm.com>

commit a44a9791e778d9ccda50d5534028ed4057a9a45b upstream.

When creating IO mappings, we lazily allocate our page tables using the
standard, non-atomic allocator functions. This presents us with a
problem, since our page tables are protected with a spinlock.

This patch reworks the smmu_domain lock to use a mutex instead of a
spinlock. iova_to_phys is then reworked so that it only reads the page
tables, and can run in a lockless fashion, leaving the mutex to guard
against concurrent mapping threads.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/iommu/arm-smmu.c | 62 +++++++++++++++++++----------------------------
1 file changed, 26 insertions(+), 36 deletions(-)

--- a/drivers/iommu/arm-smmu.c
+++ b/drivers/iommu/arm-smmu.c
@@ -392,7 +392,7 @@ struct arm_smmu_domain {
struct arm_smmu_cfg root_cfg;
phys_addr_t output_mask;

- spinlock_t lock;
+ struct mutex lock;
};

static DEFINE_SPINLOCK(arm_smmu_devices_lock);
@@ -897,7 +897,7 @@ static int arm_smmu_domain_init(struct i
goto out_free_domain;
smmu_domain->root_cfg.pgd = pgd;

- spin_lock_init(&smmu_domain->lock);
+ mutex_init(&smmu_domain->lock);
domain->priv = smmu_domain;
return 0;

@@ -1134,7 +1134,7 @@ static int arm_smmu_attach_dev(struct io
* Sanity check the domain. We don't currently support domains
* that cross between different SMMU chains.
*/
- spin_lock(&smmu_domain->lock);
+ mutex_lock(&smmu_domain->lock);
if (!smmu_domain->leaf_smmu) {
/* Now that we have a master, we can finalise the domain */
ret = arm_smmu_init_domain_context(domain, dev);
@@ -1149,7 +1149,7 @@ static int arm_smmu_attach_dev(struct io
dev_name(device_smmu->dev));
goto err_unlock;
}
- spin_unlock(&smmu_domain->lock);
+ mutex_unlock(&smmu_domain->lock);

/* Looks ok, so add the device to the domain */
master = find_smmu_master(smmu_domain->leaf_smmu, dev->of_node);
@@ -1159,7 +1159,7 @@ static int arm_smmu_attach_dev(struct io
return arm_smmu_domain_add_master(smmu_domain, master);

err_unlock:
- spin_unlock(&smmu_domain->lock);
+ mutex_unlock(&smmu_domain->lock);
return ret;
}

@@ -1388,7 +1388,7 @@ static int arm_smmu_handle_mapping(struc
if (paddr & ~output_mask)
return -ERANGE;

- spin_lock(&smmu_domain->lock);
+ mutex_lock(&smmu_domain->lock);
pgd += pgd_index(iova);
end = iova + size;
do {
@@ -1404,7 +1404,7 @@ static int arm_smmu_handle_mapping(struc
} while (pgd++, iova != end);

out_unlock:
- spin_unlock(&smmu_domain->lock);
+ mutex_unlock(&smmu_domain->lock);

/* Ensure new page tables are visible to the hardware walker */
if (smmu->features & ARM_SMMU_FEAT_COHERENT_WALK)
@@ -1443,44 +1443,34 @@ static size_t arm_smmu_unmap(struct iomm
static phys_addr_t arm_smmu_iova_to_phys(struct iommu_domain *domain,
dma_addr_t iova)
{
- pgd_t *pgd;
- pud_t *pud;
- pmd_t *pmd;
- pte_t *pte;
+ pgd_t *pgdp, pgd;
+ pud_t pud;
+ pmd_t pmd;
+ pte_t pte;
struct arm_smmu_domain *smmu_domain = domain->priv;
struct arm_smmu_cfg *root_cfg = &smmu_domain->root_cfg;
- struct arm_smmu_device *smmu = root_cfg->smmu;

- spin_lock(&smmu_domain->lock);
- pgd = root_cfg->pgd;
- if (!pgd)
- goto err_unlock;
+ pgdp = root_cfg->pgd;
+ if (!pgdp)
+ return 0;

- pgd += pgd_index(iova);
- if (pgd_none_or_clear_bad(pgd))
- goto err_unlock;
+ pgd = *(pgdp + pgd_index(iova));
+ if (pgd_none(pgd))
+ return 0;

- pud = pud_offset(pgd, iova);
- if (pud_none_or_clear_bad(pud))
- goto err_unlock;
+ pud = *pud_offset(&pgd, iova);
+ if (pud_none(pud))
+ return 0;

- pmd = pmd_offset(pud, iova);
- if (pmd_none_or_clear_bad(pmd))
- goto err_unlock;
+ pmd = *pmd_offset(&pud, iova);
+ if (pmd_none(pmd))
+ return 0;

- pte = pmd_page_vaddr(*pmd) + pte_index(iova);
+ pte = *(pmd_page_vaddr(pmd) + pte_index(iova));
if (pte_none(pte))
- goto err_unlock;
-
- spin_unlock(&smmu_domain->lock);
- return __pfn_to_phys(pte_pfn(*pte)) | (iova & ~PAGE_MASK);
+ return 0;

-err_unlock:
- spin_unlock(&smmu_domain->lock);
- dev_warn(smmu->dev,
- "invalid (corrupt?) page tables detected for iova 0x%llx\n",
- (unsigned long long)iova);
- return -EINVAL;
+ return __pfn_to_phys(pte_pfn(pte)) | (iova & ~PAGE_MASK);
}

static int arm_smmu_domain_has_cap(struct iommu_domain *domain,