If CONFIG_DEBUG=y, below assertion will be triggered:
(XEN) Assertion 'rw_is_locked(&dt_host_lock)' failed at drivers/passthrough/device_tree.c:146
(XEN) ----[ Xen-4.19-unstable  arm64  debug=y  Not tainted ]----
(XEN) CPU:    0
(XEN) PC:     00000a0000257418 iommu_remove_dt_device+0x8c/0xd4
(XEN) LR:     00000a00002573a0
(XEN) SP:     00008000fff7fb30
(XEN) CPSR:   0000000000000249 MODE:64-bit EL2h (Hypervisor, handler)
[...]

(XEN) Xen call trace:
(XEN)    [<00000a0000257418>] iommu_remove_dt_device+0x8c/0xd4 (PC)
(XEN)    [<00000a00002573a0>] iommu_remove_dt_device+0x14/0xd4 (LR)
(XEN)    [<00000a000020797c>] dt-overlay.c#remove_node_resources+0x8c/0x90
(XEN)    [<00000a0000207f14>] dt-overlay.c#remove_nodes+0x524/0x648
(XEN)    [<00000a0000208460>] dt_overlay_sysctl+0x428/0xc68
(XEN)    [<00000a00002707f8>] arch_do_sysctl+0x1c/0x2c
(XEN)    [<00000a0000230b40>] do_sysctl+0x96c/0x9ec
(XEN)    [<00000a0000271e08>] traps.c#do_trap_hypercall+0x1e8/0x288
(XEN)    [<00000a0000273490>] do_trap_guest_sync+0x448/0x63c
(XEN)    [<00000a000025c480>] entry.o#guest_sync_slowpath+0xa8/0xd8
(XEN)
(XEN)
(XEN) ****************************************
(XEN) Panic on CPU 0:
(XEN) Assertion 'rw_is_locked(&dt_host_lock)' failed at drivers/passthrough/device_tree.c:146
(XEN) ****************************************

This is because iommu_remove_dt_device() is called without taking the
dt_host_lock. Fix the issue by taking and releasing the lock properly.

Fixes: 7e5c4a8b86f1 ("xen/arm: Implement device tree node removal functionalities")
Signed-off-by: Henry Wang <xin.wang2@amd.com>
---
 xen/common/dt-overlay.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/xen/common/dt-overlay.c b/xen/common/dt-overlay.c
index 1b197381f6..39e4ba59dd 100644
--- a/xen/common/dt-overlay.c
+++ b/xen/common/dt-overlay.c
@@ -381,9 +381,14 @@ static int remove_node_resources(struct dt_device_node *device_node)
     {
         if ( dt_device_is_protected(device_node) )
         {
+            write_lock(&dt_host_lock);
             rc = iommu_remove_dt_device(device_node);
             if ( rc < 0 )
+            {
+                write_unlock(&dt_host_lock);
                 return rc;
+            }
+            write_unlock(&dt_host_lock);
         }
     }
 
-- 
2.34.1

On 24.04.2024 05:34, Henry Wang wrote:
> --- a/xen/common/dt-overlay.c
> +++ b/xen/common/dt-overlay.c
> @@ -381,9 +381,14 @@ static int remove_node_resources(struct dt_device_node *device_node)
>      {
>          if ( dt_device_is_protected(device_node) )
>          {
> +            write_lock(&dt_host_lock);
>              rc = iommu_remove_dt_device(device_node);

Any particular reason you add two call sites to the unlock function,
instead of putting it here?

Jan

>              if ( rc < 0 )
> +            {
> +                write_unlock(&dt_host_lock);
>                  return rc;
> +            }
> +            write_unlock(&dt_host_lock);
>          }
>      }
>

Hi Jan,

On 4/24/2024 1:58 PM, Jan Beulich wrote:
> On 24.04.2024 05:34, Henry Wang wrote:
>> --- a/xen/common/dt-overlay.c
>> +++ b/xen/common/dt-overlay.c
>> @@ -381,9 +381,14 @@ static int remove_node_resources(struct dt_device_node *device_node)
>>       {
>>           if ( dt_device_is_protected(device_node) )
>>           {
>> +            write_lock(&dt_host_lock);
>>               rc = iommu_remove_dt_device(device_node);
> Any particular reason you add two call sites to the unlock function,
> instead of putting it here?

Oh...you are correct. It is indeed better to put the unlock here. If 
this is the only comment for this patch, can I respin this only patch as 
a v1.1 or would one of the committers be ok to fix on commit? Sorry for 
the trouble and thanks for the suggestion.

Kind regards,
Henry

> Jan
>
>>               if ( rc < 0 )
>> +            {
>> +                write_unlock(&dt_host_lock);
>>                   return rc;
>> +            }
>> +            write_unlock(&dt_host_lock);
>>           }
>>       }
>>