[Xen-devel] [PATCH 2/2 v5] iommu/amd: Workaround for erratum 787

["Jan Beulich" <JBeulich@xxxxxxxx>]

The IOMMU interrupt handling in bottom half must clear the PPR log interrupt
and event log interrupt bits to re-enable the interrupt. This is done by
writing 1 to the memory mapped register to clear the bit. Due to hardware bug,
if the driver tries to clear this bit while the IOMMU hardware also setting
this bit, the conflict will result with the bit being set. If the interrupt
handling code does not make sure to clear this bit, subsequent changes in the
event/PPR logs will no longer generating interrupts, and would result if
buffer overflow. After clearing the bits, the driver must read back
the register to verify.

Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>

Adjust to apply on top of heavily modified patch 1. Adjust flow to get away
with a single readl() in each instance of the status register checks.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
v5: Moved most of what accumulated here into patch 1. Rather than looping,
    re-schedule the tasklet to work around the erratum.
    (skipped v4 to remain in sync with patch 1)

--- a/xen/drivers/passthrough/amd/iommu_init.c
+++ b/xen/drivers/passthrough/amd/iommu_init.c
@@ -636,6 +636,14 @@ static void iommu_check_event_log(struct
         }
     }
 
+    /*
+     * Workaround for erratum787:
+     * Re-check to make sure the bit has been cleared.
+     */
+    entry = readl(iommu->mmio_base + IOMMU_STATUS_MMIO_OFFSET);
+    if ( entry & IOMMU_STATUS_EVENT_LOG_INT_MASK )
+        tasklet_schedule(&amd_iommu_irq_tasklet);
+
     spin_unlock_irqrestore(&iommu->lock, flags);
 }
 
@@ -717,6 +725,14 @@ static void iommu_check_ppr_log(struct a
         }
     }
 
+    /*
+     * Workaround for erratum787:
+     * Re-check to make sure the bit has been cleared.
+     */
+    entry = readl(iommu->mmio_base + IOMMU_STATUS_MMIO_OFFSET);
+    if ( entry & IOMMU_STATUS_PPR_LOG_INT_MASK )
+        tasklet_schedule(&amd_iommu_irq_tasklet);
+
     spin_unlock_irqrestore(&iommu->lock, flags);
 }

Attachment: AMD-IOMMU-erratum-787-workaround
Description: Binary data

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