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Subject[PATCHv2 4/6] iommu/intel: Handle DMAR faults on workqueue
Date
dmar_fault() reports/handles/cleans DMAR faults in a cycle one-by-one.
The nuisance is that it's set as a irq handler and runs with disabled
interrupts - which works OK if you have only a couple of DMAR faults,
but becomes a problem if your intel iommu has a plenty of mappings.

We have a test that checks flapping of PCI link. Once or twice it had
stuck on soft lockup (which is panic for the typical switch):

dmar: DMAR:[DMA Write] Request device [4a:00.0] fault addr 5e1a3000
DMAR:[fault reason 02] Present bit in context entry is clear
NMI watchdog: BUG: soft lockup - CPU#8 stuck for 21s!
CPU: 8 PID: 2774 Comm: SuperServer
Call Trace:
generic_exec_single+0x11b/0x12d
? flush_tlb_func+0x0/0x18a
smp_call_function_single+0x89/0xb5
smp_call_function_many+0xef/0x207
native_flush_tlb_others+0x2e/0x30
flush_tlb_mm_range+0x139/0x18a
tlb_flush_mmu_tlbonly+0x35/0x85
tlb_flush_mmu+0x13/0x1f
tlb_finish_mmu+0x14/0x39
unmap_region+0xda/0xec
do_munmap+0x273/0x2f5
vm_munmap+0x45/0x5e
SyS_munmap+0x26/0x2f
sysenter_dispatch+0x7/0x25

Kernel panic - not syncing: softlockup: hung tasks
sending NMI to all CPUs:
NMI backtrace for cpu 0
CPU: 0 PID: 0 Comm: swapper/0
Call Trace:
<IRQ>
wait_for_xmitr+0x26/0x8f
serial8250_console_putchar+0x1c/0x2c
uart_console_write+0x40/0x4b
serial8250_console_write+0xe6/0x13f
call_console_drivers.constprop.13+0xce/0x103
console_unlock+0x1f8/0x39b
? local_clock+0x21/0x23
vprintk_emit+0x39e/0x3e6
printk+0x4d/0x4f
dmar_fault+0x1ab/0x1fd
handle_irq_event_percpu+0x8a/0x1f5
handle_irq_event+0x41/0x61
handle_edge_irq+0xe1/0xfa
handle_irq+0x155/0x166
do_IRQ+0x5a/0xea
ret_from_intr+0x0/0x15
<EOI>
arch_cpu_idle+0xf/0x11
cpu_startup_entry+0x22f/0x3cb
rest_init+0x80/0x84
start_kernel+0x470/0x47d
x86_64_start_reservations+0x2a/0x2c
x86_64_start_kernel+0x14b/0x15a

Move DMAR faults clearing out of irq-disabled critical section by
proceeding with that in a workqueue thread.
The next patch will correct the definition of dmar_fault().

Signed-off-by: Dmitry Safonov <dima@arista.com>
---
drivers/iommu/dmar.c | 48 ++++++++++++++++++++++++++++++++++++++++++++-
drivers/iommu/intel-iommu.c | 6 ++++++
include/linux/dmar.h | 1 +
3 files changed, 54 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/dmar.c b/drivers/iommu/dmar.c
index 33fb4244e438..34a53aeede38 100644
--- a/drivers/iommu/dmar.c
+++ b/drivers/iommu/dmar.c
@@ -71,6 +71,12 @@ struct acpi_table_header * __initdata dmar_tbl;
static int dmar_dev_scope_status = 1;
static unsigned long dmar_seq_ids[BITS_TO_LONGS(DMAR_UNITS_SUPPORTED)];

+static struct workqueue_struct *fault_wq;
+struct fault {
+ struct work_struct work;
+ struct intel_iommu *iommu;
+};
+
static int alloc_iommu(struct dmar_drhd_unit *drhd);
static void free_iommu(struct intel_iommu *iommu);

@@ -811,6 +817,14 @@ void __init dmar_register_bus_notifier(void)
bus_register_notifier(&pci_bus_type, &dmar_pci_bus_nb);
}

+int __init dmar_init_workqueue(void)
+{
+ fault_wq = alloc_workqueue("dmar_fault", WQ_MEM_RECLAIM | WQ_UNBOUND, 0);
+ if (fault_wq == NULL)
+ return -ENOMEM;
+
+ return 0;
+}

int __init dmar_table_init(void)
{
@@ -1695,6 +1709,38 @@ irqreturn_t dmar_fault(int irq, void *dev_id)
return IRQ_HANDLED;
}

+static void dmar_fault_work(struct work_struct *work)
+{
+ struct fault *fault = container_of(work, struct fault, work);
+
+ dmar_fault(-1, (void*)fault->iommu);
+}
+
+static irqreturn_t dmar_fault_handler(int irq, void *dev_id)
+{
+ struct intel_iommu *iommu = dev_id;
+ struct fault *fault;
+
+ fault = kzalloc(sizeof(*fault), GFP_ATOMIC);
+ if (fault == NULL) {
+ unsigned long flag;
+
+ /* During OOM - clear faults and let device re-fault */
+ raw_spin_lock_irqsave(&iommu->register_lock, flag);
+ clear_primary_faults(iommu);
+ raw_spin_unlock_irqrestore(&iommu->register_lock, flag);
+
+ return IRQ_HANDLED;
+ }
+
+ fault->iommu = iommu;
+ INIT_WORK(&fault->work, dmar_fault_work);
+
+ queue_work(fault_wq, &fault->work);
+
+ return IRQ_HANDLED;
+}
+
int dmar_set_interrupt(struct intel_iommu *iommu)
{
int irq, ret;
@@ -1713,7 +1759,7 @@ int dmar_set_interrupt(struct intel_iommu *iommu)
return -EINVAL;
}

- ret = request_irq(irq, dmar_fault, IRQF_NO_THREAD, iommu->name, iommu);
+ ret = request_irq(irq, dmar_fault_handler, IRQF_NO_THREAD, iommu->name, iommu);
if (ret)
pr_err("Can't request irq\n");
return ret;
diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index 582fd01cb7d1..64ad9786f5b9 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -4783,6 +4783,12 @@ int __init intel_iommu_init(void)
goto out_free_dmar;
}

+ if (dmar_init_workqueue()) {
+ if (force_on)
+ panic("tboot: Failed to init workqueue for DMARs\n");
+ goto out_free_dmar;
+ }
+
if (list_empty(&dmar_rmrr_units))
pr_info("No RMRR found\n");

diff --git a/include/linux/dmar.h b/include/linux/dmar.h
index e2433bc50210..5de4932a6ad8 100644
--- a/include/linux/dmar.h
+++ b/include/linux/dmar.h
@@ -113,6 +113,7 @@ static inline bool dmar_rcu_check(void)
extern int dmar_table_init(void);
extern int dmar_dev_scope_init(void);
extern void dmar_register_bus_notifier(void);
+extern int dmar_init_workqueue(void);
extern int dmar_parse_dev_scope(void *start, void *end, int *cnt,
struct dmar_dev_scope **devices, u16 segment);
extern void *dmar_alloc_dev_scope(void *start, void *end, int *cnt);
--
2.13.6
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