From df42a04b15f19a842393dc98a84cbc52b1f8ed49 Mon Sep 17 00:00:00 2001 From: Scott Wood Date: Wed, 14 Feb 2018 17:36:28 -0600 Subject: [PATCH] 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: Scott Wood Signed-off-by: Joerg Roedel --- drivers/iommu/amd_iommu.c | 29 ++++++++++++++++++++++------- 1 file changed, 22 insertions(+), 7 deletions(-) diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c index d666246ac30b..14efeb306a9f 100644 --- a/drivers/iommu/amd_iommu.c +++ b/drivers/iommu/amd_iommu.c @@ -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;