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[Xen-devel] [PATCH v9 1/3] VT-d: add a command line parameter for Queued Invalidation

The command line parameter 'vtd_qi_timeout' specifies the
timeout of the VT-d Queued Invalidation in milliseconds. By
default, the timeout is 1ms, which can be boot-time changed.

Add a __must_check annotation. The followup patch titled
'VT-d IOTLB/Context/IEC flush issue' addresses the __mustcheck.
That is the other callers of this routine (two or three
levels up) ignore the return code. This patch does not
address this but the other does.

Signed-off-by: Quan Xu <quan.xu@xxxxxxxxx>
 docs/misc/xen-command-line.markdown  | 18 ++++++++++++++++++
 xen/drivers/passthrough/vtd/qinval.c | 17 ++++++++++++-----
 2 files changed, 30 insertions(+), 5 deletions(-)

diff --git a/docs/misc/xen-command-line.markdown 
index ca77e3b..5a7ed5d 100644
--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -1532,6 +1532,24 @@ Note that if **watchdog** option is also specified vpmu 
will be turned off.
 As the virtualisation is not 100% safe, don't use the vpmu flag on
 production systems (see http://xenbits.xen.org/xsa/advisory-163.html)!
+### vtd\_qi\_timeout (VT-d)
+> `= <integer>`
+> Default: `1`
+Specify the timeout of the VT-d Queued Invalidation in milliseconds.
+By default, the spin timeout is 1ms, which can be boot-time changed.
+In current code, VT-d Queued Invalidation includes Device-TLB, IOTLB,
+Context and IEC flush. If Device-TLB flush timed out, we would hide
+the target ATS device and crash the domain owning this ATS device.
+If impacted domain is hardware domain, just throw out a warning (done
+in queue\_invalidate\_wait). IOTLB, Context and IEC flush timeout are
+still in TODO-list.
+When you see error 'Queue invalidate wait descriptor timed out', try
+increasing the vtd\_qi\_timeout to 10ms or more.
 ### watchdog
 > `= force | <boolean>`
diff --git a/xen/drivers/passthrough/vtd/qinval.c 
index b81b0bd..52ba2c2 100644
--- a/xen/drivers/passthrough/vtd/qinval.c
+++ b/xen/drivers/passthrough/vtd/qinval.c
@@ -28,6 +28,11 @@
 #include "vtd.h"
 #include "extern.h"
+static unsigned int __read_mostly vtd_qi_timeout = 1;
+integer_param("vtd_qi_timeout", vtd_qi_timeout);
+#define IOMMU_QI_TIMEOUT (vtd_qi_timeout * MILLISECS(1))
 static void print_qi_regs(struct iommu *iommu)
     u64 val;
@@ -130,10 +135,10 @@ static void queue_invalidate_iotlb(struct iommu *iommu,
     spin_unlock_irqrestore(&iommu->register_lock, flags);
-static int queue_invalidate_wait(struct iommu *iommu,
+static int __must_check queue_invalidate_wait(struct iommu *iommu,
     u8 iflag, u8 sw, u8 fn)
-    s_time_t start_time;
+    s_time_t timeout;
     volatile u32 poll_slot = QINVAL_STAT_INIT;
     unsigned int index;
     unsigned long flags;
@@ -164,13 +169,15 @@ static int queue_invalidate_wait(struct iommu *iommu,
     if ( sw )
         /* In case all wait descriptor writes to same addr with same data */
-        start_time = NOW();
+        timeout = NOW() + IOMMU_QI_TIMEOUT;
         while ( poll_slot != QINVAL_STAT_DONE )
-            if ( NOW() > (start_time + DMAR_OPERATION_TIMEOUT) )
+            if ( NOW() > timeout )
-                panic("queue invalidate wait descriptor was not executed");
+                printk(XENLOG_WARNING VTDPREFIX
+                       "Queue invalidate wait descriptor timed out.\n");
+                return -ETIMEDOUT;

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