linux-kernel - [PATCH 2/3] iommu/vt-d: Replace spin_lock with mutex to protect domain ida

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Message-ID: <20250423031020.2189546-3-baolu.lu@linux.intel.com>
Date: Wed, 23 Apr 2025 11:10:19 +0800
From: Lu Baolu <baolu.lu@...ux.intel.com>
To: Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>,
	Robin Murphy <robin.murphy@....com>,
	Jason Gunthorpe <jgg@...pe.ca>,
	Kevin Tian <kevin.tian@...el.com>
Cc: iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	Lu Baolu <baolu.lu@...ux.intel.com>
Subject: [PATCH 2/3] iommu/vt-d: Replace spin_lock with mutex to protect domain ida

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@...ux.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 0afba7434a5c..e25e8d3dedcb 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 76e170922149..3a9ea0ad2cd3 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -1347,17 +1347,16 @@ 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, FLPT_DEFAULT_DID + 1,
-			      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;
@@ -1367,19 +1366,17 @@ 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;
 }
@@ -1391,7 +1388,7 @@ 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);
@@ -1399,7 +1396,6 @@ 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 993232292400..1e98c10ca553 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