[PATCH] device-tree: Move Arm's static-evtchn feature to common

[PATCH] device-tree: Move Arm's static-evtchn feature to common

[Michal Orzel]

There's nothing Arm specific about this feature. Move it to common as
part of a larger activity to commonalize device tree related features.
For now, select it only for ARM until others (e.g. RISC-V) verify it
works for them too.

Signed-off-by: Michal Orzel <michal.orzel@amd.com>
---
Other candidates: static memory, shared memory
---
 xen/arch/arm/Kconfig                                      | 8 --------
 xen/arch/arm/Makefile                                     | 1 -
 xen/arch/arm/setup.c                                      | 2 +-
 xen/common/Kconfig                                        | 8 ++++++++
 xen/common/device-tree/Makefile                           | 1 +
 xen/{arch/arm => common/device-tree}/static-evtchn.c      | 3 +--
 xen/{arch/arm/include/asm => include/xen}/static-evtchn.h | 6 +++---
 7 files changed, 14 insertions(+), 15 deletions(-)
 rename xen/{arch/arm => common/device-tree}/static-evtchn.c (99%)
 rename xen/{arch/arm/include/asm => include/xen}/static-evtchn.h (77%)

diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig
index a5aad97a688e..57919d8b3ac8 100644
--- a/xen/arch/arm/Kconfig
+++ b/xen/arch/arm/Kconfig
@@ -253,14 +253,6 @@ config STATIC_SHM
 	help
 	  This option enables statically shared memory on a dom0less system.
 
-config STATIC_EVTCHN
-	bool "Static event channel support on a dom0less system"
-	depends on DOM0LESS_BOOT
-	default y
-	help
-	  This option enables establishing static event channel communication
-	  between domains on a dom0less system (domU-domU as well as domU-dom0).
-
 config PARTIAL_EMULATION
 	bool "Enable partial emulation of system/coprocessor registers"
 	default y
diff --git a/xen/arch/arm/Makefile b/xen/arch/arm/Makefile
index 129a109d6ec5..eeeac4e653ec 100644
--- a/xen/arch/arm/Makefile
+++ b/xen/arch/arm/Makefile
@@ -51,7 +51,6 @@ obj-y += setup.o
 obj-y += shutdown.o
 obj-y += smp.o
 obj-y += smpboot.o
-obj-$(CONFIG_STATIC_EVTCHN) += static-evtchn.init.o
 obj-$(CONFIG_STATIC_MEMORY) += static-memory.init.o
 obj-$(CONFIG_STATIC_SHM) += static-shmem.init.o
 obj-y += sysctl.o
diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
index 10b46d068405..734e23da4408 100644
--- a/xen/arch/arm/setup.c
+++ b/xen/arch/arm/setup.c
@@ -31,6 +31,7 @@
 #include <xen/version.h>
 #include <xen/vmap.h>
 #include <xen/stack-protector.h>
+#include <xen/static-evtchn.h>
 #include <xen/trace.h>
 #include <xen/libfdt/libfdt-xen.h>
 #include <xen/acpi.h>
@@ -39,7 +40,6 @@
 #include <asm/alternative.h>
 #include <asm/dom0less-build.h>
 #include <asm/page.h>
-#include <asm/static-evtchn.h>
 #include <asm/current.h>
 #include <asm/setup.h>
 #include <asm/gic.h>
diff --git a/xen/common/Kconfig b/xen/common/Kconfig
index 3d66d0939738..0951d4c2f286 100644
--- a/xen/common/Kconfig
+++ b/xen/common/Kconfig
@@ -162,6 +162,14 @@ config STATIC_MEMORY
 
 	  If unsure, say N.
 
+config STATIC_EVTCHN
+	bool "Static event channel support on a dom0less system"
+	depends on DOM0LESS_BOOT && ARM
+	default y
+	help
+	  This option enables establishing static event channel communication
+	  between domains on a dom0less system (domU-domU as well as domU-dom0).
+
 menu "Speculative hardening"
 
 config INDIRECT_THUNK
diff --git a/xen/common/device-tree/Makefile b/xen/common/device-tree/Makefile
index 831b91399b74..2df7eb27222e 100644
--- a/xen/common/device-tree/Makefile
+++ b/xen/common/device-tree/Makefile
@@ -6,3 +6,4 @@ obj-$(CONFIG_DOM0LESS_BOOT) += dom0less-build.o
 obj-$(CONFIG_OVERLAY_DTB) += dt-overlay.o
 obj-y += intc.o
 obj-$(CONFIG_DOMAIN_BUILD_HELPERS) += kernel.o
+obj-$(CONFIG_STATIC_EVTCHN) += static-evtchn.init.o
diff --git a/xen/arch/arm/static-evtchn.c b/xen/common/device-tree/static-evtchn.c
similarity index 99%
rename from xen/arch/arm/static-evtchn.c
rename to xen/common/device-tree/static-evtchn.c
index 49db08d5c6fc..8b82e6b3d8a6 100644
--- a/xen/arch/arm/static-evtchn.c
+++ b/xen/common/device-tree/static-evtchn.c
@@ -1,8 +1,7 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
 #include <xen/event.h>
-
-#include <asm/static-evtchn.h>
+#include <xen/static-evtchn.h>
 
 #define STATIC_EVTCHN_NODE_SIZE_CELLS 2
 
diff --git a/xen/arch/arm/include/asm/static-evtchn.h b/xen/include/xen/static-evtchn.h
similarity index 77%
rename from xen/arch/arm/include/asm/static-evtchn.h
rename to xen/include/xen/static-evtchn.h
index f964522f6a62..31ae92741aad 100644
--- a/xen/arch/arm/include/asm/static-evtchn.h
+++ b/xen/include/xen/static-evtchn.h
@@ -1,7 +1,7 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
-#ifndef __ASM_STATIC_EVTCHN_H_
-#define __ASM_STATIC_EVTCHN_H_
+#ifndef XEN_STATIC_EVTCHN_H
+#define XEN_STATIC_EVTCHN_H
 
 #ifdef CONFIG_STATIC_EVTCHN
 
@@ -13,7 +13,7 @@ static inline void alloc_static_evtchn(void) {};
 
 #endif /* CONFIG_STATIC_EVTCHN */
 
-#endif /* __ASM_STATIC_EVTCHN_H_ */
+#endif /* XEN_STATIC_EVTCHN_H */
 
 /*
  * Local variables:
-- 
2.25.1

Re: [PATCH] device-tree: Move Arm's static-evtchn feature to common

[Stefano Stabellini]

On Tue, 27 May 2025, Michal Orzel wrote:
> There's nothing Arm specific about this feature. Move it to common as
> part of a larger activity to commonalize device tree related features.
> For now, select it only for ARM until others (e.g. RISC-V) verify it
> works for them too.
> 
> Signed-off-by: Michal Orzel <michal.orzel@amd.com>

Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>


> ---
> Other candidates: static memory, shared memory
> ---
>  xen/arch/arm/Kconfig                                      | 8 --------
>  xen/arch/arm/Makefile                                     | 1 -
>  xen/arch/arm/setup.c                                      | 2 +-
>  xen/common/Kconfig                                        | 8 ++++++++
>  xen/common/device-tree/Makefile                           | 1 +
>  xen/{arch/arm => common/device-tree}/static-evtchn.c      | 3 +--
>  xen/{arch/arm/include/asm => include/xen}/static-evtchn.h | 6 +++---
>  7 files changed, 14 insertions(+), 15 deletions(-)
>  rename xen/{arch/arm => common/device-tree}/static-evtchn.c (99%)
>  rename xen/{arch/arm/include/asm => include/xen}/static-evtchn.h (77%)
> 
> diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig
> index a5aad97a688e..57919d8b3ac8 100644
> --- a/xen/arch/arm/Kconfig
> +++ b/xen/arch/arm/Kconfig
> @@ -253,14 +253,6 @@ config STATIC_SHM
>  	help
>  	  This option enables statically shared memory on a dom0less system.
>  
> -config STATIC_EVTCHN
> -	bool "Static event channel support on a dom0less system"
> -	depends on DOM0LESS_BOOT
> -	default y
> -	help
> -	  This option enables establishing static event channel communication
> -	  between domains on a dom0less system (domU-domU as well as domU-dom0).
> -
>  config PARTIAL_EMULATION
>  	bool "Enable partial emulation of system/coprocessor registers"
>  	default y
> diff --git a/xen/arch/arm/Makefile b/xen/arch/arm/Makefile
> index 129a109d6ec5..eeeac4e653ec 100644
> --- a/xen/arch/arm/Makefile
> +++ b/xen/arch/arm/Makefile
> @@ -51,7 +51,6 @@ obj-y += setup.o
>  obj-y += shutdown.o
>  obj-y += smp.o
>  obj-y += smpboot.o
> -obj-$(CONFIG_STATIC_EVTCHN) += static-evtchn.init.o
>  obj-$(CONFIG_STATIC_MEMORY) += static-memory.init.o
>  obj-$(CONFIG_STATIC_SHM) += static-shmem.init.o
>  obj-y += sysctl.o
> diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
> index 10b46d068405..734e23da4408 100644
> --- a/xen/arch/arm/setup.c
> +++ b/xen/arch/arm/setup.c
> @@ -31,6 +31,7 @@
>  #include <xen/version.h>
>  #include <xen/vmap.h>
>  #include <xen/stack-protector.h>
> +#include <xen/static-evtchn.h>
>  #include <xen/trace.h>
>  #include <xen/libfdt/libfdt-xen.h>
>  #include <xen/acpi.h>
> @@ -39,7 +40,6 @@
>  #include <asm/alternative.h>
>  #include <asm/dom0less-build.h>
>  #include <asm/page.h>
> -#include <asm/static-evtchn.h>
>  #include <asm/current.h>
>  #include <asm/setup.h>
>  #include <asm/gic.h>
> diff --git a/xen/common/Kconfig b/xen/common/Kconfig
> index 3d66d0939738..0951d4c2f286 100644
> --- a/xen/common/Kconfig
> +++ b/xen/common/Kconfig
> @@ -162,6 +162,14 @@ config STATIC_MEMORY
>  
>  	  If unsure, say N.
>  
> +config STATIC_EVTCHN
> +	bool "Static event channel support on a dom0less system"
> +	depends on DOM0LESS_BOOT && ARM
> +	default y
> +	help
> +	  This option enables establishing static event channel communication
> +	  between domains on a dom0less system (domU-domU as well as domU-dom0).
> +
>  menu "Speculative hardening"
>  
>  config INDIRECT_THUNK
> diff --git a/xen/common/device-tree/Makefile b/xen/common/device-tree/Makefile
> index 831b91399b74..2df7eb27222e 100644
> --- a/xen/common/device-tree/Makefile
> +++ b/xen/common/device-tree/Makefile
> @@ -6,3 +6,4 @@ obj-$(CONFIG_DOM0LESS_BOOT) += dom0less-build.o
>  obj-$(CONFIG_OVERLAY_DTB) += dt-overlay.o
>  obj-y += intc.o
>  obj-$(CONFIG_DOMAIN_BUILD_HELPERS) += kernel.o
> +obj-$(CONFIG_STATIC_EVTCHN) += static-evtchn.init.o
> diff --git a/xen/arch/arm/static-evtchn.c b/xen/common/device-tree/static-evtchn.c
> similarity index 99%
> rename from xen/arch/arm/static-evtchn.c
> rename to xen/common/device-tree/static-evtchn.c
> index 49db08d5c6fc..8b82e6b3d8a6 100644
> --- a/xen/arch/arm/static-evtchn.c
> +++ b/xen/common/device-tree/static-evtchn.c
> @@ -1,8 +1,7 @@
>  /* SPDX-License-Identifier: GPL-2.0-only */
>  
>  #include <xen/event.h>
> -
> -#include <asm/static-evtchn.h>
> +#include <xen/static-evtchn.h>
>  
>  #define STATIC_EVTCHN_NODE_SIZE_CELLS 2
>  
> diff --git a/xen/arch/arm/include/asm/static-evtchn.h b/xen/include/xen/static-evtchn.h
> similarity index 77%
> rename from xen/arch/arm/include/asm/static-evtchn.h
> rename to xen/include/xen/static-evtchn.h
> index f964522f6a62..31ae92741aad 100644
> --- a/xen/arch/arm/include/asm/static-evtchn.h
> +++ b/xen/include/xen/static-evtchn.h
> @@ -1,7 +1,7 @@
>  /* SPDX-License-Identifier: GPL-2.0-only */
>  
> -#ifndef __ASM_STATIC_EVTCHN_H_
> -#define __ASM_STATIC_EVTCHN_H_
> +#ifndef XEN_STATIC_EVTCHN_H
> +#define XEN_STATIC_EVTCHN_H
>  
>  #ifdef CONFIG_STATIC_EVTCHN
>  
> @@ -13,7 +13,7 @@ static inline void alloc_static_evtchn(void) {};
>  
>  #endif /* CONFIG_STATIC_EVTCHN */
>  
> -#endif /* __ASM_STATIC_EVTCHN_H_ */
> +#endif /* XEN_STATIC_EVTCHN_H */
>  
>  /*
>   * Local variables:
> -- 
> 2.25.1
> 

Re: [PATCH] device-tree: Move Arm's static-evtchn feature to common

[Jan Beulich]

On 27.05.2025 10:21, Michal Orzel wrote:
> There's nothing Arm specific about this feature. Move it to common as
> part of a larger activity to commonalize device tree related features.
> For now, select it only for ARM until others (e.g. RISC-V) verify it
> works for them too.
> 
> Signed-off-by: Michal Orzel <michal.orzel@amd.com>

I realize this was already committed, but ...

> --- a/xen/common/Kconfig
> +++ b/xen/common/Kconfig
> @@ -162,6 +162,14 @@ config STATIC_MEMORY
>  
>  	  If unsure, say N.
>  
> +config STATIC_EVTCHN
> +	bool "Static event channel support on a dom0less system"
> +	depends on DOM0LESS_BOOT && ARM

... I think we should strive to avoid such arch dependencies; they simply
don't scale very well. Instead (if needed) HAS_* should be introduced, which
each interested arch can select. In the case here, however, perhaps
DOM0LESS_BOOT alone would have been sufficient as a dependency?

Jan

Re: [PATCH] device-tree: Move Arm's static-evtchn feature to common

[Orzel, Michal]

On 02/06/2025 10:37, Jan Beulich wrote:
> On 27.05.2025 10:21, Michal Orzel wrote:
>> There's nothing Arm specific about this feature. Move it to common as
>> part of a larger activity to commonalize device tree related features.
>> For now, select it only for ARM until others (e.g. RISC-V) verify it
>> works for them too.
>>
>> Signed-off-by: Michal Orzel <michal.orzel@amd.com>
> 
> I realize this was already committed, but ...
> 
>> --- a/xen/common/Kconfig
>> +++ b/xen/common/Kconfig
>> @@ -162,6 +162,14 @@ config STATIC_MEMORY
>>  
>>  	  If unsure, say N.
>>  
>> +config STATIC_EVTCHN
>> +	bool "Static event channel support on a dom0less system"
>> +	depends on DOM0LESS_BOOT && ARM
> 
> ... I think we should strive to avoid such arch dependencies; they simply
> don't scale very well. Instead (if needed) HAS_* should be introduced, which
> each interested arch can select. In the case here, however, perhaps
> DOM0LESS_BOOT alone would have been sufficient as a dependency?
What if e.g. RISC-V wants to enable dom0less but not static evtchn/memory/shmem
because there are some functions to be implemented and they don't want to do it
now? Protecting with just DOM0LESS_BOOT would not be sufficient here. I
understand we could define HAS_*. I did not think about it.

~Michal

Re: [PATCH] device-tree: Move Arm's static-evtchn feature to common

[Jan Beulich]

On 03.06.2025 08:54, Orzel, Michal wrote:
> 
> 
> On 02/06/2025 10:37, Jan Beulich wrote:
>> On 27.05.2025 10:21, Michal Orzel wrote:
>>> There's nothing Arm specific about this feature. Move it to common as
>>> part of a larger activity to commonalize device tree related features.
>>> For now, select it only for ARM until others (e.g. RISC-V) verify it
>>> works for them too.
>>>
>>> Signed-off-by: Michal Orzel <michal.orzel@amd.com>
>>
>> I realize this was already committed, but ...
>>
>>> --- a/xen/common/Kconfig
>>> +++ b/xen/common/Kconfig
>>> @@ -162,6 +162,14 @@ config STATIC_MEMORY
>>>  
>>>  	  If unsure, say N.
>>>  
>>> +config STATIC_EVTCHN
>>> +	bool "Static event channel support on a dom0less system"
>>> +	depends on DOM0LESS_BOOT && ARM
>>
>> ... I think we should strive to avoid such arch dependencies; they simply
>> don't scale very well. Instead (if needed) HAS_* should be introduced, which
>> each interested arch can select. In the case here, however, perhaps
>> DOM0LESS_BOOT alone would have been sufficient as a dependency?
> What if e.g. RISC-V wants to enable dom0less but not static evtchn/memory/shmem
> because there are some functions to be implemented and they don't want to do it
> now? Protecting with just DOM0LESS_BOOT would not be sufficient here.

Imo a transient(!) "depends on !RISCV" would in principle be fine, if ...

> I understand we could define HAS_*. I did not think about it.

... we don't want to go this route.

Jan

Re: [PATCH] device-tree: Move Arm's static-evtchn feature to common

[Orzel, Michal]

On 03/06/2025 09:02, Jan Beulich wrote:
> On 03.06.2025 08:54, Orzel, Michal wrote:
>>
>>
>> On 02/06/2025 10:37, Jan Beulich wrote:
>>> On 27.05.2025 10:21, Michal Orzel wrote:
>>>> There's nothing Arm specific about this feature. Move it to common as
>>>> part of a larger activity to commonalize device tree related features.
>>>> For now, select it only for ARM until others (e.g. RISC-V) verify it
>>>> works for them too.
>>>>
>>>> Signed-off-by: Michal Orzel <michal.orzel@amd.com>
>>>
>>> I realize this was already committed, but ...
>>>
>>>> --- a/xen/common/Kconfig
>>>> +++ b/xen/common/Kconfig
>>>> @@ -162,6 +162,14 @@ config STATIC_MEMORY
>>>>  
>>>>  	  If unsure, say N.
>>>>  
>>>> +config STATIC_EVTCHN
>>>> +	bool "Static event channel support on a dom0less system"
>>>> +	depends on DOM0LESS_BOOT && ARM
>>>
>>> ... I think we should strive to avoid such arch dependencies; they simply
>>> don't scale very well. Instead (if needed) HAS_* should be introduced, which
>>> each interested arch can select. In the case here, however, perhaps
>>> DOM0LESS_BOOT alone would have been sufficient as a dependency?
>> What if e.g. RISC-V wants to enable dom0less but not static evtchn/memory/shmem
>> because there are some functions to be implemented and they don't want to do it
>> now? Protecting with just DOM0LESS_BOOT would not be sufficient here.
> 
> Imo a transient(!) "depends on !RISCV" would in principle be fine, if ...
In this case, how can I know that upfront? When moving a feature I need to put
some dependencies. At that point I don't know RISCV, PPC plans. The only thing I
know is that I tested this feature on Arm. So the only meaningful dependency is
& ARM.

~Michal

Re: [PATCH] device-tree: Move Arm's static-evtchn feature to common

[Jan Beulich]

On 03.06.2025 09:06, Orzel, Michal wrote:
> 
> 
> On 03/06/2025 09:02, Jan Beulich wrote:
>> On 03.06.2025 08:54, Orzel, Michal wrote:
>>>
>>>
>>> On 02/06/2025 10:37, Jan Beulich wrote:
>>>> On 27.05.2025 10:21, Michal Orzel wrote:
>>>>> There's nothing Arm specific about this feature. Move it to common as
>>>>> part of a larger activity to commonalize device tree related features.
>>>>> For now, select it only for ARM until others (e.g. RISC-V) verify it
>>>>> works for them too.
>>>>>
>>>>> Signed-off-by: Michal Orzel <michal.orzel@amd.com>
>>>>
>>>> I realize this was already committed, but ...
>>>>
>>>>> --- a/xen/common/Kconfig
>>>>> +++ b/xen/common/Kconfig
>>>>> @@ -162,6 +162,14 @@ config STATIC_MEMORY
>>>>>  
>>>>>  	  If unsure, say N.
>>>>>  
>>>>> +config STATIC_EVTCHN
>>>>> +	bool "Static event channel support on a dom0less system"
>>>>> +	depends on DOM0LESS_BOOT && ARM
>>>>
>>>> ... I think we should strive to avoid such arch dependencies; they simply
>>>> don't scale very well. Instead (if needed) HAS_* should be introduced, which
>>>> each interested arch can select. In the case here, however, perhaps
>>>> DOM0LESS_BOOT alone would have been sufficient as a dependency?
>>> What if e.g. RISC-V wants to enable dom0less but not static evtchn/memory/shmem
>>> because there are some functions to be implemented and they don't want to do it
>>> now? Protecting with just DOM0LESS_BOOT would not be sufficient here.
>>
>> Imo a transient(!) "depends on !RISCV" would in principle be fine, if ...
> In this case, how can I know that upfront? When moving a feature I need to put
> some dependencies. At that point I don't know RISCV, PPC plans.

You don't need to know this up front, do you? Neither of the two presently selects
DOM0LESS_BOOT afaict, and hence such a transient negative dependency would (if
necessary in the first place) be added when adding such a select.

Jan

Re: [PATCH] device-tree: Move Arm's static-evtchn feature to common

[Orzel, Michal]

On 03/06/2025 09:09, Jan Beulich wrote:
> On 03.06.2025 09:06, Orzel, Michal wrote:
>>
>>
>> On 03/06/2025 09:02, Jan Beulich wrote:
>>> On 03.06.2025 08:54, Orzel, Michal wrote:
>>>>
>>>>
>>>> On 02/06/2025 10:37, Jan Beulich wrote:
>>>>> On 27.05.2025 10:21, Michal Orzel wrote:
>>>>>> There's nothing Arm specific about this feature. Move it to common as
>>>>>> part of a larger activity to commonalize device tree related features.
>>>>>> For now, select it only for ARM until others (e.g. RISC-V) verify it
>>>>>> works for them too.
>>>>>>
>>>>>> Signed-off-by: Michal Orzel <michal.orzel@amd.com>
>>>>>
>>>>> I realize this was already committed, but ...
>>>>>
>>>>>> --- a/xen/common/Kconfig
>>>>>> +++ b/xen/common/Kconfig
>>>>>> @@ -162,6 +162,14 @@ config STATIC_MEMORY
>>>>>>  
>>>>>>  	  If unsure, say N.
>>>>>>  
>>>>>> +config STATIC_EVTCHN
>>>>>> +	bool "Static event channel support on a dom0less system"
>>>>>> +	depends on DOM0LESS_BOOT && ARM
>>>>>
>>>>> ... I think we should strive to avoid such arch dependencies; they simply
>>>>> don't scale very well. Instead (if needed) HAS_* should be introduced, which
>>>>> each interested arch can select. In the case here, however, perhaps
>>>>> DOM0LESS_BOOT alone would have been sufficient as a dependency?
>>>> What if e.g. RISC-V wants to enable dom0less but not static evtchn/memory/shmem
>>>> because there are some functions to be implemented and they don't want to do it
>>>> now? Protecting with just DOM0LESS_BOOT would not be sufficient here.
>>>
>>> Imo a transient(!) "depends on !RISCV" would in principle be fine, if ...
>> In this case, how can I know that upfront? When moving a feature I need to put
>> some dependencies. At that point I don't know RISCV, PPC plans.
> 
> You don't need to know this up front, do you? Neither of the two presently selects
> DOM0LESS_BOOT afaict, and hence such a transient negative dependency would (if
> necessary in the first place) be added when adding such a select.
Ok, so basically this should be left to people adding support for DOM0LESS_BOOT
for other arches in the future.

There is static mem and shmem left to be moved. I think we can squeeze in a
patch removing && ARM in this case.

~Michal