118 lines
3.7 KiB
Diff
118 lines
3.7 KiB
Diff
From: Scott Wood <swood@redhat.com>
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Date: Wed, 14 Feb 2018 17:36:28 -0600
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Subject: [PATCH 3/3] iommu/amd: Avoid locking get_irq_table() from atomic
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context
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.16/older/patches-4.16.7-rt1.tar.xz
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Upstream commit df42a04b15f19a842393dc98a84cbc52b1f8ed49
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get_irq_table() previously acquired amd_iommu_devtable_lock which is not
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a raw lock, and thus cannot be acquired from atomic context on
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PREEMPT_RT. Many calls to modify_irte*() come from atomic context due to
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the IRQ desc->lock, as does amd_iommu_update_ga() due to the preemption
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disabling in vcpu_load/put().
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The only difference between calling get_irq_table() and reading from
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irq_lookup_table[] directly, other than the lock acquisition and
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amd_iommu_rlookup_table[] check, is if the table entry is unpopulated,
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which should never happen when looking up a devid that came from an
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irq_2_irte struct, as get_irq_table() would have already been called on
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that devid during irq_remapping_alloc().
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The lock acquisition is not needed in these cases because entries in
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irq_lookup_table[] never change once non-NULL -- nor would the
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amd_iommu_devtable_lock usage in get_irq_table() provide meaningful
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protection if they did, since it's released before using the looked up
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table in the get_irq_table() caller.
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Rename the old get_irq_table() to alloc_irq_table(), and create a new
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lockless get_irq_table() to be used in non-allocating contexts that WARNs
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if it doesn't find what it's looking for.
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Signed-off-by: Scott Wood <swood@redhat.com>
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Signed-off-by: Joerg Roedel <jroedel@suse.de>
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---
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drivers/iommu/amd_iommu.c | 29 ++++++++++++++++++++++-------
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1 file changed, 22 insertions(+), 7 deletions(-)
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--- a/drivers/iommu/amd_iommu.c
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+++ b/drivers/iommu/amd_iommu.c
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@@ -3595,7 +3595,22 @@ static void set_dte_irq_entry(u16 devid,
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amd_iommu_dev_table[devid].data[2] = dte;
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}
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-static struct irq_remap_table *get_irq_table(u16 devid, bool ioapic)
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+static struct irq_remap_table *get_irq_table(u16 devid)
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+{
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+ struct irq_remap_table *table;
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+
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+ if (WARN_ONCE(!amd_iommu_rlookup_table[devid],
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+ "%s: no iommu for devid %x\n", __func__, devid))
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+ return NULL;
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+
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+ table = irq_lookup_table[devid];
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+ if (WARN_ONCE(!table, "%s: no table for devid %x\n", __func__, devid))
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+ return NULL;
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+
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+ return table;
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+}
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+
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+static struct irq_remap_table *alloc_irq_table(u16 devid, bool ioapic)
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{
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struct irq_remap_table *table = NULL;
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struct amd_iommu *iommu;
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@@ -3682,7 +3697,7 @@ static int alloc_irq_index(u16 devid, in
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if (!iommu)
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return -ENODEV;
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- table = get_irq_table(devid, false);
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+ table = alloc_irq_table(devid, false);
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if (!table)
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return -ENODEV;
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@@ -3733,7 +3748,7 @@ static int modify_irte_ga(u16 devid, int
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if (iommu == NULL)
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return -EINVAL;
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- table = get_irq_table(devid, false);
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+ table = get_irq_table(devid);
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if (!table)
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return -ENOMEM;
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@@ -3766,7 +3781,7 @@ static int modify_irte(u16 devid, int in
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if (iommu == NULL)
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return -EINVAL;
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- table = get_irq_table(devid, false);
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+ table = get_irq_table(devid);
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if (!table)
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return -ENOMEM;
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@@ -3790,7 +3805,7 @@ static void free_irte(u16 devid, int ind
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if (iommu == NULL)
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return;
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- table = get_irq_table(devid, false);
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+ table = get_irq_table(devid);
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if (!table)
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return;
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@@ -4108,7 +4123,7 @@ static int irq_remapping_alloc(struct ir
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return ret;
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if (info->type == X86_IRQ_ALLOC_TYPE_IOAPIC) {
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- if (get_irq_table(devid, true))
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+ if (alloc_irq_table(devid, true))
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index = info->ioapic_pin;
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else
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ret = -ENOMEM;
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@@ -4391,7 +4406,7 @@ int amd_iommu_update_ga(int cpu, bool is
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if (!iommu)
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return -ENODEV;
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- irt = get_irq_table(devid, false);
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+ irt = get_irq_table(devid);
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if (!irt)
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return -ENODEV;
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