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Subject[PATCH 09/10] iommu/amd: drop the lock while allocating new irq remap table
Date
The irq_remap_table is allocated while the iommu_table_lock is held with
interrupts disabled. While this works it makes RT scream very loudly.
From looking at the call sites, all callers are in the early device
initialisation (apic_bsp_setup(), pci_enable_device(),
pci_enable_msi()) so make sense to drop the lock which also enables
interrupts and try to allocate that memory with GFP_KERNEL instead
GFP_ATOMIC.

Since during the allocation the iommu_table_lock is dropped, we need to
recheck if table exists after the lock has been reacquired. I *think*
that it is impossible that the "devid" entry appears in irq_lookup_table
while the lock is dropped since the same device can only be probed once.
It is more likely that another device added an `alias' entry. However I
check for both cases, just to be sure.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
drivers/iommu/amd_iommu.c | 65 +++++++++++++++++++++++++++++++++--------------
1 file changed, 46 insertions(+), 19 deletions(-)

diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
index 7dd4c27a941d..0a7ca5e95288 100644
--- a/drivers/iommu/amd_iommu.c
+++ b/drivers/iommu/amd_iommu.c
@@ -3602,6 +3602,30 @@ static void set_dte_irq_entry(u16 devid, struct irq_remap_table *table)
amd_iommu_dev_table[devid].data[2] = dte;
}

+static struct irq_remap_table *alloc_irq_table(void)
+{
+ struct irq_remap_table *table;
+
+ table = kzalloc(sizeof(*table), GFP_ATOMIC);
+ if (!table)
+ return NULL;
+
+ table->table = kmem_cache_alloc(amd_iommu_irq_cache, GFP_KERNEL);
+ if (!table->table) {
+ kfree(table);
+ return NULL;
+ }
+ raw_spin_lock_init(&table->lock);
+
+ if (!AMD_IOMMU_GUEST_IR_GA(amd_iommu_guest_ir))
+ memset(table->table, 0,
+ MAX_IRQS_PER_TABLE * sizeof(u32));
+ else
+ memset(table->table, 0,
+ (MAX_IRQS_PER_TABLE * (sizeof(u64) * 2)));
+ return table;
+}
+
static void set_remap_table_entry(struct amd_iommu *iommu, u16 devid,
struct irq_remap_table *table)
{
@@ -3613,6 +3637,7 @@ static void set_remap_table_entry(struct amd_iommu *iommu, u16 devid,
static struct irq_remap_table *get_irq_table(u16 devid)
{
struct irq_remap_table *table = NULL;
+ struct irq_remap_table *new_table = NULL;
struct amd_iommu *iommu;
unsigned long flags;
u16 alias;
@@ -3631,42 +3656,44 @@ static struct irq_remap_table *get_irq_table(u16 devid)
table = irq_lookup_table[alias];
if (table) {
set_remap_table_entry(iommu, devid, table);
- goto out;
+ goto out_wait;
}
+ raw_spin_unlock_irqrestore(&iommu_table_lock, flags);

/* Nothing there yet, allocate new irq remapping table */
- table = kzalloc(sizeof(*table), GFP_ATOMIC);
- if (!table)
+ new_table = alloc_irq_table();
+ if (!new_table)
+ return NULL;
+
+ raw_spin_lock_irqsave(&iommu_table_lock, flags);
+
+ table = irq_lookup_table[devid];
+ if (table)
goto out_unlock;

- /* Initialize table spin-lock */
- raw_spin_lock_init(&table->lock);
-
- table->table = kmem_cache_alloc(amd_iommu_irq_cache, GFP_ATOMIC);
- if (!table->table) {
- kfree(table);
- table = NULL;
- goto out_unlock;
+ table = irq_lookup_table[alias];
+ if (table) {
+ set_remap_table_entry(iommu, devid, table);
+ goto out_wait;
}

- if (!AMD_IOMMU_GUEST_IR_GA(amd_iommu_guest_ir))
- memset(table->table, 0,
- MAX_IRQS_PER_TABLE * sizeof(u32));
- else
- memset(table->table, 0,
- (MAX_IRQS_PER_TABLE * (sizeof(u64) * 2)));
-
+ table = new_table;
+ new_table = NULL;

set_remap_table_entry(iommu, devid, table);
if (devid != alias)
set_remap_table_entry(iommu, alias, table);

-out:
+out_wait:
iommu_completion_wait(iommu);

out_unlock:
raw_spin_unlock_irqrestore(&iommu_table_lock, flags);

+ if (new_table) {
+ kmem_cache_free(amd_iommu_irq_cache, new_table->table);
+ kfree(new_table);
+ }
return table;
}

--
2.16.2
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