[PATCH 2/6] xen/arm: domain_build: Inherit GIC's interrupt-parent from host device tree

[Chris Patterson <cjp256@gmail.com>]

From: "Chris Patterson" <pattersonc@ainfosec.com>

Currently, the interrupt parent is left undefined during creation in
make_gic_node().  In cases where a non-GIC interrupt controller is present,
this can lead to incorrect assignment of interrupt parents.

On the Tegra, the gic's interrupt parent is set to itself:

	gic: interrupt-controller@0,50041000 {
		compatible = "arm,gic-400";
		#interrupt-cells = <3>;
		interrupt-controller;
		reg = <0x0 0x50041000 0x0 0x1000>,
		      <0x0 0x50042000 0x0 0x2000>,
		      <0x0 0x50044000 0x0 0x2000>,
		      <0x0 0x50046000 0x0 0x2000>;
		interrupts = <GIC_PPI 9
			(GIC_CPU_MASK_SIMPLE(4) | IRQ_TYPE_LEVEL_HIGH)>;
		interrupt-parent = <&gic>;
	};

To prevent the hardware domain from assuming the Legacy Interrupt Controller
(lic) as the GIC's interrupt-parent, this change explicitly assigns
the interrupt-parent property from the host device tree.

Authored-by: Kyle Temkin <temkink@ainfosec.com>
Signed-off-by: Kyle Temkin <temkink@ainfosec.com>
Signed-off-by: Chris Patterson <pattersonc@ainfosec.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
---

changes from rfc:
- commit message documentation improvements

---
 xen/arch/arm/domain_build.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index de59e5f..cb66304 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -778,8 +778,8 @@ static int make_gic_node(const struct domain *d, void *fdt,
 {
     const struct dt_device_node *gic = dt_interrupt_controller;
     int res = 0;
-    const void *addrcells, *sizecells;
-    u32 addrcells_len, sizecells_len;
+    const void *addrcells, *sizecells, *iparent;
+    u32 addrcells_len, sizecells_len, iparent_len;
 
     /*
      * Xen currently supports only a single GIC. Discard any secondary
@@ -809,6 +809,19 @@ static int make_gic_node(const struct domain *d, void *fdt,
             return res;
     }
 
+    /*
+     * If available, explicitly inherit interrupt-parent property from host
+     * device tree.  This will prevent the risk of incorrect identification
+     * of the parent on platforms with more than one interrupt controller.
+     */
+    iparent = dt_get_property(gic, "interrupt-parent", &iparent_len);
+    if ( iparent )
+    {
+        res = fdt_property(fdt, "interrupt-parent", iparent, iparent_len);
+        if ( res )
+          return res;
+    }
+
     addrcells = dt_get_property(gic, "#address-cells", &addrcells_len);
     if ( addrcells )
     {
-- 
2.1.4


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