[Xen-devel] [PATCH] x86/iommu: add comment regarding setting of need_sync

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

Clarify why relaxed hardware domains don't need iommu page-table
syncing.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
Cc: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/drivers/passthrough/iommu.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/xen/drivers/passthrough/iommu.c b/xen/drivers/passthrough/iommu.c
index 79ec6719f5..f8c3bf53bd 100644
--- a/xen/drivers/passthrough/iommu.c
+++ b/xen/drivers/passthrough/iommu.c
@@ -185,6 +185,10 @@ void __hwdom_init iommu_hwdom_init(struct domain *d)
     register_keyhandler('o', &iommu_dump_p2m_table, "dump iommu p2m table", 0);
 
     hd->status = IOMMU_STATUS_initializing;
+    /*
+     * NB: relaxed hw domains don't need sync because all ram is already
+     * mapped in the iommu page tables.
+     */
     hd->need_sync = iommu_hwdom_strict && !iommu_use_hap_pt(d);
     if ( need_iommu_pt_sync(d) )
     {
-- 
2.20.1 (Apple Git-117)


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