[xen staging] xen/arm: dom0less: Add trap-unmapped-accesses

[patchbot@xxxxxxx]

commit 5f91a9b209cb8a7ecf353ccdb836a73761b9e2e3
Author:     Edgar E. Iglesias <edgar.iglesias@xxxxxxx>
AuthorDate: Mon Jun 16 17:38:23 2025 +0200
Commit:     Stefano Stabellini <stefano.stabellini@xxxxxxx>
CommitDate: Tue Jun 17 10:59:04 2025 -0700

    xen/arm: dom0less: Add trap-unmapped-accesses
    
    Add the trap-unmapped-accesses per-domain fdt property.
    
    Signed-off-by: Edgar E. Iglesias <edgar.iglesias@xxxxxxx>
    Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
---
 docs/misc/arm/device-tree/booting.txt | 10 ++++++++++
 xen/arch/arm/dom0less-build.c         |  9 ++++++++-
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/docs/misc/arm/device-tree/booting.txt 
b/docs/misc/arm/device-tree/booting.txt
index 59fa96a82e..07acc7ba64 100644
--- a/docs/misc/arm/device-tree/booting.txt
+++ b/docs/misc/arm/device-tree/booting.txt
@@ -225,6 +225,16 @@ with the following properties:
     option is provided with a non zero value, but the platform doesn't support
     SVE.
 
+- trap-unmapped-accesses
+
+    Optional. An integer that configures handling of accesses to unmapped
+    address ranges.
+    If set to 0, guest accesses will read all bits as ones, e.g 0xFFFFFFFF
+    for a 32bit access and writes will be ignored.
+    If set to 1, guest accesses will trap.
+
+    The default is 1 when trap-unmapped-accesses is absent.
+
 - xen,enhanced
 
     A string property. Possible property values are:
diff --git a/xen/arch/arm/dom0less-build.c b/xen/arch/arm/dom0less-build.c
index 981af5079f..4b285cff5e 100644
--- a/xen/arch/arm/dom0less-build.c
+++ b/xen/arch/arm/dom0less-build.c
@@ -344,8 +344,15 @@ void __init arch_create_domUs(struct dt_device_node *node,
 #endif
     }
 
-    /* Trap accesses to unmapped areas. */
+    /* Trap unmapped accesses by default. */
     d_cfg->flags |= XEN_DOMCTL_CDF_trap_unmapped_accesses;
+    if ( dt_property_read_u32(node, "trap-unmapped-accesses", &val) )
+    {
+        if ( val > 1 )
+            panic("trap-unmapped-accesses: supported values are 0 or 1");
+        if ( !val )
+            d_cfg->flags &= ~XEN_DOMCTL_CDF_trap_unmapped_accesses;
+    }
 }
 
 int __init init_intc_phandle(struct kernel_info *kinfo, const char *name,
--
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