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[Xen-devel] [PATCH 2/2] VT-d: reconcile iommu_inclusive_mapping and iommu=dom0-strict

The documentation for the iommu_inclusive_mapping Xen command line option

"Use this to work around firmware issues providing incorrect RMRR entries"

Unfortunately this workaround does not function correctly if the dom0-strict
iommu option is also specified.

The documentation goes on to say:

"Rather than only mapping RAM pages for IOMMU accesses for Dom0, with this
 option all pages up to and including 4GB, not marked as unusable in the
 E820 table, will get a  mapping established."

This patch modifies the VT-d hardware domain initialization code such that
the workaround will continue to function in dom0-strict mode, by mapping
all pages not marked as unusable *unless* they are RAM pages not assigned
to dom0.

Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Julien Grall <julien.grall@xxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Tim Deegan <tim@xxxxxxx>
Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
Cc: Kevin Tian <kevin.tian@xxxxxxxxx>
 docs/misc/xen-command-line.markdown   | 4 +++-
 xen/drivers/passthrough/iommu.c       | 2 +-
 xen/drivers/passthrough/vtd/iommu.c   | 2 +-
 xen/drivers/passthrough/vtd/x86/vtd.c | 8 ++++++++
 xen/include/xen/iommu.h               | 2 +-
 5 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/docs/misc/xen-command-line.markdown 
index 6beb28dada..97768f1633 100644
--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -1213,7 +1213,9 @@ wait descriptor timed out', try increasing this value.
 Use this to work around firmware issues providing incorrect RMRR entries.
 Rather than only mapping RAM pages for IOMMU accesses for Dom0, with this
 option all pages up to and including 4GB, not marked as unusable in the
-E820 table, will get a mapping established.
+E820 table, will get a mapping established. Note that if `dom0-strict`
+mode is enabled then conventional RAM pages not assigned to dom0 will not
+be mapped.
 ### irq\_ratelimit (x86)
 > `= <integer>`
diff --git a/xen/drivers/passthrough/iommu.c b/xen/drivers/passthrough/iommu.c
index 2c44fabf99..a483212356 100644
--- a/xen/drivers/passthrough/iommu.c
+++ b/xen/drivers/passthrough/iommu.c
@@ -52,7 +52,7 @@ custom_param("iommu", parse_iommu_param);
 bool_t __initdata iommu_enable = 1;
 bool_t __read_mostly iommu_enabled;
 bool_t __read_mostly force_iommu;
-bool_t __hwdom_initdata iommu_dom0_strict;
+bool_t __read_mostly iommu_dom0_strict;
 bool_t __read_mostly iommu_verbose;
 bool_t __read_mostly iommu_workaround_bios_bug;
 bool_t __read_mostly iommu_igfx = 1;
diff --git a/xen/drivers/passthrough/vtd/iommu.c 
index 08bce92d40..e3f043288b 100644
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -1304,7 +1304,7 @@ static void __hwdom_init intel_iommu_hwdom_init(struct 
domain *d)
     struct acpi_drhd_unit *drhd;
-    if ( !iommu_passthrough && !need_iommu(d) )
+    if ( !iommu_passthrough )
         /* Set up 1:1 page table for hardware domain. */
diff --git a/xen/drivers/passthrough/vtd/x86/vtd.c 
index 5c440ba183..42a8c7901d 100644
--- a/xen/drivers/passthrough/vtd/x86/vtd.c
+++ b/xen/drivers/passthrough/vtd/x86/vtd.c
@@ -144,6 +144,14 @@ void __hwdom_init vtd_set_hwdom_mapping(struct domain *d)
         if ( xen_in_range(pfn) )
+        /*
+         * If dom0-strict mode is enabled then exclude conventional RAM
+         * and let the common code map dom0's pages.
+         */
+        if ( iommu_dom0_strict &&
+             page_is_ram_type(pfn, RAM_TYPE_CONVENTIONAL) )
+            continue;
         tmp = 1 << (PAGE_SHIFT - PAGE_SHIFT_4K);
         for ( j = 0; j < tmp; j++ )
diff --git a/xen/include/xen/iommu.h b/xen/include/xen/iommu.h
index 33c8b221dc..6b42e3b876 100644
--- a/xen/include/xen/iommu.h
+++ b/xen/include/xen/iommu.h
@@ -29,7 +29,7 @@
 #include <asm/iommu.h>
 extern bool_t iommu_enable, iommu_enabled;
-extern bool_t force_iommu, iommu_verbose;
+extern bool_t force_iommu, iommu_dom0_strict, iommu_verbose;
 extern bool_t iommu_workaround_bios_bug, iommu_igfx, iommu_passthrough;
 extern bool_t iommu_snoop, iommu_qinval, iommu_intremap, iommu_intpost;
 extern bool_t iommu_hap_pt_share;

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