From: Roger Pau Monné <roger.pau@citrix.com>
Date: Tue, 23 Jul 2019 15:00:07 +0000 (+0200)
Subject: x86/iommu: add comment regarding setting of need_sync
X-Git-Tag: archive/raspbian/4.14.0+80-gd101b417b7-1+rpi1^2~63^2~1862
X-Git-Url: https://dgit.raspbian.org/%22http://www.example.com/cgi/%22/%22http:/www.example.com/cgi/%22?a=commitdiff_plain;h=52fc4aaf1613e49d018bf3c5b1899b131ee2f417;p=xen.git

x86/iommu: add comment regarding setting of need_sync

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

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
---

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) )
     {