[Xen-devel] PATCH 1 of 2] Move IOMMU faults handling into softirq for VT-d.

[Dario Faggioli <raistlin@xxxxxxxx>]

Dealing with interrupts from VT-d IOMMU is deferred to a
softirq-tasklet, raised by the actual IRQ handler. Since a new interrupt
is not generated, even if further faults occur, until we cleared all the
pending ones, there's no need to disabling IRQs, as the hardware does it
by its own. Notice that this may cause the log to overflow, but none of
the existing entry will be overwritten.

Signed-off-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx>

diff -r a4bffc85bb71 xen/drivers/passthrough/vtd/iommu.c
--- a/xen/drivers/passthrough/vtd/iommu.c       Mon Dec 19 09:37:52 2011 +0100
+++ b/xen/drivers/passthrough/vtd/iommu.c       Mon Dec 19 16:46:14 2011 +0000
@@ -53,6 +53,8 @@ bool_t __read_mostly untrusted_msi;
 
 int nr_iommus;
 
+static struct tasklet vtd_fault_tasklet;
+
 static void setup_dom0_device(struct pci_dev *);
 static void setup_dom0_rmrr(struct domain *d);
 
@@ -918,10 +920,8 @@ static void iommu_fault_status(u32 fault
 }
 
 #define PRIMARY_FAULT_REG_LEN (16)
-static void iommu_page_fault(int irq, void *dev_id,
-                             struct cpu_user_regs *regs)
+static void __do_iommu_page_fault(struct iommu *iommu)
 {
-    struct iommu *iommu = dev_id;
     int reg, fault_index;
     u32 fault_status;
     unsigned long flags;
@@ -996,6 +996,33 @@ clear_overflow:
     }
 }
 
+static void do_iommu_page_fault(unsigned long data)
+{
+    struct acpi_drhd_unit *drhd;
+
+    if ( list_empty(&acpi_drhd_units) )
+    {
+       INTEL_IOMMU_DEBUG("no device found, something must be very wrong!\n");
+       return;
+    }
+
+    /* No matter from whom the interrupt came from, check all the
+     * IOMMUs present in the system. This allows for having just one
+     * tasklet (instead of one per each IOMMU) and should be more than
+     * fine, considering how rare the event of a fault should be. */
+    for_each_drhd_unit ( drhd )
+        __do_iommu_page_fault(drhd->iommu);
+}
+
+static void iommu_page_fault(int irq, void *dev_id,
+                             struct cpu_user_regs *regs)
+{
+    /* Just flag the tasklet as runnable. This is fine, according to VT-d
+     * specs since a new interrupt won't be generated until we clear all
+     * the faults that caused this one to happen. */
+    tasklet_schedule(&vtd_fault_tasklet);
+}
+
 static void dma_msi_unmask(struct irq_desc *desc)
 {
     struct iommu *iommu = desc->action->dev_id;
@@ -2144,6 +2171,8 @@ int __init intel_vtd_setup(void)
         iommu->irq = ret;
     }
 
+    softirq_tasklet_init(&vtd_fault_tasklet, do_iommu_page_fault, 0);
+
     if ( !iommu_qinval && iommu_intremap )
     {
         iommu_intremap = 0;


-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-------------------------------------------------------------------
Dario Faggioli, http://retis.sssup.it/people/faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)
PhD Candidate, ReTiS Lab, Scuola Superiore Sant'Anna, Pisa (Italy)

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