From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Thu, 22 Mar 2018 16:22:41 +0100
Subject: iommu/amd: Make amd_iommu_devtable_lock a spin_lock
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
Git-commit: 52c18ef2972427c3400c10f1f9b61e5f965087ca
Patch-mainline: Queued in subsystem maintainer repository
References: SLE Realtime Extension

Upstream commit 2cd1083d79a0a8c223af430ca97884c28a1e2fc0

Before commit 0bb6e243d7fb ("iommu/amd: Support IOMMU_DOMAIN_DMA type
allocation") amd_iommu_devtable_lock had a read_lock() user but now
there are none. In fact, after the mentioned commit we had only
write_lock() user of the lock. Since there is no reason to keep it as
writer lock, change its type to a spin_lock.
I *think* that we might even be able to remove the lock because all its
current user seem to have their own protection.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Mike Galbraith <mgalbraith@suse.de>
---
 drivers/iommu/amd_iommu.c |   14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

--- a/drivers/iommu/amd_iommu.c
+++ b/drivers/iommu/amd_iommu.c
@@ -79,7 +79,7 @@
  */
 #define AMD_IOMMU_PGSIZES	((~0xFFFUL) & ~(2ULL << 38))
 
-static DEFINE_RWLOCK(amd_iommu_devtable_lock);
+static DEFINE_SPINLOCK(amd_iommu_devtable_lock);
 static DEFINE_SPINLOCK(pd_bitmap_lock);
 static DEFINE_SPINLOCK(iommu_table_lock);
 
@@ -2294,9 +2294,9 @@ static int attach_device(struct device *
 	}
 
 skip_ats_check:
-	write_lock_irqsave(&amd_iommu_devtable_lock, flags);
+	spin_lock_irqsave(&amd_iommu_devtable_lock, flags);
 	ret = __attach_device(dev_data, domain);
-	write_unlock_irqrestore(&amd_iommu_devtable_lock, flags);
+	spin_unlock_irqrestore(&amd_iommu_devtable_lock, flags);
 
 	/*
 	 * We might boot into a crash-kernel here. The crashed kernel
@@ -2346,9 +2346,9 @@ static void detach_device(struct device
 	domain   = dev_data->domain;
 
 	/* lock device table */
-	write_lock_irqsave(&amd_iommu_devtable_lock, flags);
+	spin_lock_irqsave(&amd_iommu_devtable_lock, flags);
 	__detach_device(dev_data);
-	write_unlock_irqrestore(&amd_iommu_devtable_lock, flags);
+	spin_unlock_irqrestore(&amd_iommu_devtable_lock, flags);
 
 	if (!dev_is_pci(dev))
 		return;
@@ -3003,7 +3003,7 @@ static void cleanup_domain(struct protec
 	struct iommu_dev_data *entry;
 	unsigned long flags;
 
-	write_lock_irqsave(&amd_iommu_devtable_lock, flags);
+	spin_lock_irqsave(&amd_iommu_devtable_lock, flags);
 
 	while (!list_empty(&domain->dev_list)) {
 		entry = list_first_entry(&domain->dev_list,
@@ -3011,7 +3011,7 @@ static void cleanup_domain(struct protec
 		__detach_device(entry);
 	}
 
-	write_unlock_irqrestore(&amd_iommu_devtable_lock, flags);
+	spin_unlock_irqrestore(&amd_iommu_devtable_lock, flags);
 }
 
 static void protection_domain_free(struct protection_domain *domain)