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Commit df42a04b authored by Scott Wood's avatar Scott Wood Committed by Joerg Roedel
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iommu/amd: Avoid locking get_irq_table() from atomic context 



get_irq_table() previously acquired amd_iommu_devtable_lock which is not
a raw lock, and thus cannot be acquired from atomic context on
PREEMPT_RT.  Many calls to modify_irte*() come from atomic context due to
the IRQ desc->lock, as does amd_iommu_update_ga() due to the preemption
disabling in vcpu_load/put().

The only difference between calling get_irq_table() and reading from
irq_lookup_table[] directly, other than the lock acquisition and
amd_iommu_rlookup_table[] check, is if the table entry is unpopulated,
which should never happen when looking up a devid that came from an
irq_2_irte struct, as get_irq_table() would have already been called on
that devid during irq_remapping_alloc().

The lock acquisition is not needed in these cases because entries in
irq_lookup_table[] never change once non-NULL -- nor would the
amd_iommu_devtable_lock usage in get_irq_table() provide meaningful
protection if they did, since it's released before using the looked up
table in the get_irq_table() caller.

Rename the old get_irq_table() to alloc_irq_table(), and create a new
lockless get_irq_table() to be used in non-allocating contexts that WARNs
if it doesn't find what it's looking for.

Signed-off-by: default avatarScott Wood <swood@redhat.com>
Signed-off-by: default avatarJoerg Roedel <jroedel@suse.de>
parent 01ee04ba

drivers/iommu/amd_iommu.c

+22 −7
Original line number Diff line number Diff line
@@ -3595,7 +3595,22 @@ 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 *get_irq_table(u16 devid, bool ioapic)

static struct irq_remap_table *get_irq_table(u16 devid)

{

	struct irq_remap_table *table;



	if (WARN_ONCE(!amd_iommu_rlookup_table[devid],

		      "%s: no iommu for devid %x\n", __func__, devid))

		return NULL;



	table = irq_lookup_table[devid];

	if (WARN_ONCE(!table, "%s: no table for devid %x\n", __func__, devid))

		return NULL;



	return table;

}



static struct irq_remap_table *alloc_irq_table(u16 devid, bool ioapic)

{

	struct irq_remap_table *table = NULL;

	struct amd_iommu *iommu;
@@ -3682,7 +3697,7 @@ static int alloc_irq_index(u16 devid, int count, bool align) 
	if (!iommu)

		return -ENODEV;



	table = get_irq_table(devid, false);

	table = alloc_irq_table(devid, false);

	if (!table)

		return -ENODEV;
@@ -3733,7 +3748,7 @@ static int modify_irte_ga(u16 devid, int index, struct irte_ga *irte, 
	if (iommu == NULL)

		return -EINVAL;



	table = get_irq_table(devid, false);

	table = get_irq_table(devid);

	if (!table)

		return -ENOMEM;
@@ -3766,7 +3781,7 @@ static int modify_irte(u16 devid, int index, union irte *irte) 
	if (iommu == NULL)

		return -EINVAL;



	table = get_irq_table(devid, false);

	table = get_irq_table(devid);

	if (!table)

		return -ENOMEM;
@@ -3790,7 +3805,7 @@ static void free_irte(u16 devid, int index) 
	if (iommu == NULL)

		return;



	table = get_irq_table(devid, false);

	table = get_irq_table(devid);

	if (!table)

		return;
@@ -4108,7 +4123,7 @@ static int irq_remapping_alloc(struct irq_domain *domain, unsigned int virq, 
		return ret;



	if (info->type == X86_IRQ_ALLOC_TYPE_IOAPIC) {

		if (get_irq_table(devid, true))

		if (alloc_irq_table(devid, true))

			index = info->ioapic_pin;

		else

			ret = -ENOMEM;
@@ -4391,7 +4406,7 @@ int amd_iommu_update_ga(int cpu, bool is_run, void *data) 
	if (!iommu)

		return -ENODEV;



	irt = get_irq_table(devid, false);

	irt = get_irq_table(devid);

	if (!irt)

		return -ENODEV;