irqchip/gic-v3-its: Plug allocation race for devices sharing a DevID

On systems or VMs where multiple devices share a single DevID
(because they sit behind a PCI bridge, or because the HW is
broken in funky ways), we reuse the save its_device structure
in order to reflect this.

It turns out that there is a distinct lack of locking when looking
up the its_device, and two device being probed concurrently can result
in double allocations. That's obviously not nice.

A solution for this is to have a per-ITS mutex that serializes device
allocation.

A similar issue exists on the freeing side, which can run concurrently
with the allocation. On top of now taking the appropriate lock, we
also make sure that a shared device is never freed, as we have no way
to currently track the life cycle of such object.

Reported-by: Zheng Xiang <zhengxiang9@huawei.com>
Tested-by: Zheng Xiang <zhengxiang9@huawei.com>
Cc: stable@vger.kernel.org
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

1 files changed, 27 insertions, 5 deletions

diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
index 36181197d5e0..f25ec92f23ee 100644
--- a/drivers/irqchip/irq-gic-v3-its.c
+++ b/drivers/irqchip/irq-gic-v3-its.c
@@ -97,9 +97,14 @@ struct its_device;
  * The ITS structure - contains most of the infrastructure, with the
  * top-level MSI domain, the command queue, the collections, and the
  * list of devices writing to it.
+ *
+ * dev_alloc_lock has to be taken for device allocations, while the
+ * spinlock must be taken to parse data structures such as the device
+ * list.
  */
 struct its_node {
         raw_spinlock_t          lock;
+        struct mutex            dev_alloc_lock;
         struct list_head        entry;
         void __iomem            *base;
         phys_addr_t             phys_base;
@@ -156,6 +161,7 @@ struct its_device {
         void                    *itt;
         u32                     nr_ites;
         u32                     device_id;
+        bool                    shared;
 };
 
 static struct {
@@ -2469,6 +2475,7 @@ static int its_msi_prepare(struct irq_domain *domain, struct device *dev,
         struct its_device *its_dev;
         struct msi_domain_info *msi_info;
         u32 dev_id;
+        int err = 0;
 
         /*
          * We ignore "dev" entierely, and rely on the dev_id that has
@@ -2491,6 +2498,7 @@ static int its_msi_prepare(struct irq_domain *domain, struct device *dev,
                 return -EINVAL;
         }
 
+        mutex_lock(&its->dev_alloc_lock);
         its_dev = its_find_device(its, dev_id);
         if (its_dev) {
                 /*
@@ -2498,18 +2506,22 @@ static int its_msi_prepare(struct irq_domain *domain, struct device *dev,
                  * another alias (PCI bridge of some sort). No need to
                  * create the device.
                  */
+                its_dev->shared = true;
                 pr_debug("Reusing ITT for devID %x\n", dev_id);
                 goto out;
         }
 
         its_dev = its_create_device(its, dev_id, nvec, true);
-        if (!its_dev)
-                return -ENOMEM;
+        if (!its_dev) {
+                err = -ENOMEM;
+                goto out;
+        }
 
         pr_debug("ITT %d entries, %d bits\n", nvec, ilog2(nvec));
 out:
+        mutex_unlock(&its->dev_alloc_lock);
         info->scratchpad[0].ptr = its_dev;
-        return 0;
+        return err;
 }
 
 static struct msi_domain_ops its_msi_domain_ops = {
@@ -2613,6 +2625,7 @@ static void its_irq_domain_free(struct irq_domain *domain, unsigned int virq,
 {
         struct irq_data *d = irq_domain_get_irq_data(domain, virq);
         struct its_device *its_dev = irq_data_get_irq_chip_data(d);
+        struct its_node *its = its_dev->its;
         int i;
 
         for (i = 0; i < nr_irqs; i++) {
@@ -2627,8 +2640,14 @@ static void its_irq_domain_free(struct irq_domain *domain, unsigned int virq,
                 irq_domain_reset_irq_data(data);
         }
 
-        /* If all interrupts have been freed, start mopping the floor */
-        if (bitmap_empty(its_dev->event_map.lpi_map,
+        mutex_lock(&its->dev_alloc_lock);
+
+        /*
+         * If all interrupts have been freed, start mopping the
+         * floor. This is conditionned on the device not being shared.
+         */
+        if (!its_dev->shared &&
+            bitmap_empty(its_dev->event_map.lpi_map,
                          its_dev->event_map.nr_lpis)) {
                 its_lpi_free(its_dev->event_map.lpi_map,
                              its_dev->event_map.lpi_base,
@@ -2640,6 +2659,8 @@ static void its_irq_domain_free(struct irq_domain *domain, unsigned int virq,
                 its_free_device(its_dev);
         }
 
+        mutex_unlock(&its->dev_alloc_lock);
+
         irq_domain_free_irqs_parent(domain, virq, nr_irqs);
 }
 
@@ -3549,6 +3570,7 @@ static int __init its_probe_one(struct resource *res,
         }
 
         raw_spin_lock_init(&its->lock);
+        mutex_init(&its->dev_alloc_lock);
         INIT_LIST_HEAD(&its->entry);
         INIT_LIST_HEAD(&its->its_device_list);
         typer = gic_read_typer(its_base + GITS_TYPER);