[PATCH 3/5] iommu/vt-d: Replace spin_lock with mutex to protect domain ida

[Lu Baolu <baolu.lu@linux.intel.com>]

The domain ID allocator is currently protected by a spin_lock. However,
ida_alloc_range can potentially block if it needs to allocate memory to
grow its internal structures.

Replace the spin_lock with a mutex which allows sleep on block. Thus,
the memory allocation flags can be updated from GFP_ATOMIC to GFP_KERNEL
to allow blocking memory allocations if necessary.

Introduce a new mutex, did_lock, specifically for protecting the domain
ida. The existing spinlock will remain for protecting other intel_iommu
fields.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20250430021135.2370244-3-baolu.lu@linux.intel.com
---
 drivers/iommu/intel/dmar.c  |  1 +
 drivers/iommu/intel/iommu.c | 12 ++++--------
 drivers/iommu/intel/iommu.h |  2 ++
 3 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/drivers/iommu/intel/dmar.c b/drivers/iommu/intel/dmar.c
index 0e35969c026b..9e17e8e56308 100644
--- a/drivers/iommu/intel/dmar.c
+++ b/drivers/iommu/intel/dmar.c
@@ -1101,6 +1101,7 @@ static int alloc_iommu(struct dmar_drhd_unit *drhd)
 	iommu->node = NUMA_NO_NODE;
 	spin_lock_init(&iommu->lock);
 	ida_init(&iommu->domain_ida);
+	mutex_init(&iommu->did_lock);
 
 	ver = readl(iommu->reg + DMAR_VER_REG);
 	pr_info("%s: reg_base_addr %llx ver %d:%d cap %llx ecap %llx\n",
diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 0cac6b00adb0..8c405532ddbf 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -1345,17 +1345,16 @@ int domain_attach_iommu(struct dmar_domain *domain, struct intel_iommu *iommu)
 	if (!info)
 		return -ENOMEM;
 
-	spin_lock(&iommu->lock);
+	guard(mutex)(&iommu->did_lock);
 	curr = xa_load(&domain->iommu_array, iommu->seq_id);
 	if (curr) {
 		curr->refcnt++;
-		spin_unlock(&iommu->lock);
 		kfree(info);
 		return 0;
 	}
 
 	num = ida_alloc_range(&iommu->domain_ida, IDA_START_DID,
-			      cap_ndoms(iommu->cap) - 1, GFP_ATOMIC);
+			      cap_ndoms(iommu->cap) - 1, GFP_KERNEL);
 	if (num < 0) {
 		pr_err("%s: No free domain ids\n", iommu->name);
 		goto err_unlock;
@@ -1365,19 +1364,17 @@ int domain_attach_iommu(struct dmar_domain *domain, struct intel_iommu *iommu)
 	info->did	= num;
 	info->iommu	= iommu;
 	curr = xa_cmpxchg(&domain->iommu_array, iommu->seq_id,
-			  NULL, info, GFP_ATOMIC);
+			  NULL, info, GFP_KERNEL);
 	if (curr) {
 		ret = xa_err(curr) ? : -EBUSY;
 		goto err_clear;
 	}
 
-	spin_unlock(&iommu->lock);
 	return 0;
 
 err_clear:
 	ida_free(&iommu->domain_ida, info->did);
 err_unlock:
-	spin_unlock(&iommu->lock);
 	kfree(info);
 	return ret;
 }
@@ -1389,7 +1386,7 @@ void domain_detach_iommu(struct dmar_domain *domain, struct intel_iommu *iommu)
 	if (domain->domain.type == IOMMU_DOMAIN_SVA)
 		return;
 
-	spin_lock(&iommu->lock);
+	guard(mutex)(&iommu->did_lock);
 	info = xa_load(&domain->iommu_array, iommu->seq_id);
 	if (--info->refcnt == 0) {
 		ida_free(&iommu->domain_ida, info->did);
@@ -1397,7 +1394,6 @@ void domain_detach_iommu(struct dmar_domain *domain, struct intel_iommu *iommu)
 		domain->nid = NUMA_NO_NODE;
 		kfree(info);
 	}
-	spin_unlock(&iommu->lock);
 }
 
 static void domain_exit(struct dmar_domain *domain)
diff --git a/drivers/iommu/intel/iommu.h b/drivers/iommu/intel/iommu.h
index 25faf3aadd24..5f140892fae0 100644
--- a/drivers/iommu/intel/iommu.h
+++ b/drivers/iommu/intel/iommu.h
@@ -722,6 +722,8 @@ struct intel_iommu {
 	unsigned char	name[16];    /* Device Name */
 
 #ifdef CONFIG_INTEL_IOMMU
+	/* mutex to protect domain_ida */
+	struct mutex	did_lock;
 	struct ida	domain_ida; /* domain id allocator */
 	unsigned long	*copied_tables; /* bitmap of copied tables */
 	spinlock_t	lock; /* protect context, domain ids */
-- 
2.43.0