[PATCH v2 1/2] cpu/hotplug: Fix build error of using {add,remove}_cpu() with !CONFIG_SMP

[PATCH v2 1/2] cpu/hotplug: Fix build error of using {add,remove}_cpu() with !CONFIG_SMP

[shuo.a.liu]

From: Shuo Liu <shuo.a.liu@intel.com>

279dcf693ac7 ("virt: acrn: Introduce an interface for Service VM to
control vCPU") introduced {add,remove}_cpu() usage and it hit below
error with !CONFIG_SMP:

../drivers/virt/acrn/hsm.c: In function ‘remove_cpu_store’:
../drivers/virt/acrn/hsm.c:389:3: error: implicit declaration of function ‘remove_cpu’; [-Werror=implicit-function-declaration]
   remove_cpu(cpu);

../drivers/virt/acrn/hsm.c:402:2: error: implicit declaration of function ‘add_cpu’; [-Werror=implicit-function-declaration]
   add_cpu(cpu);

Add add_cpu() function prototypes with !CONFIG_SMP and remove_cpu() with
!CONFIG_HOTPLUG_CPU for such usage.

Fixes: 279dcf693ac7 ("virt: acrn: Introduce an interface for Service VM to control vCPU")
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Shuo Liu <shuo.a.liu@intel.com>
---
I followed Greg's idea that add {add,remove}_cpu() functions prototypes.
The v2 solution is different from the v1, so i removed Randy's Acked-by.
Randy, please help have a look on v2.

v2:
  - Drop the #ifdef in .c solution. Add {add,remove}_cpu() prototypes. (Suggested by Greg)

 include/linux/cpu.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index 3aaa0687e8df..94a578a96202 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -108,6 +108,8 @@ static inline void cpu_maps_update_done(void)
 {
 }
 
+static inline int add_cpu(unsigned int cpu) { return 0;}
+
 #endif /* CONFIG_SMP */
 extern struct bus_type cpu_subsys;
 
@@ -137,6 +139,7 @@ static inline int  cpus_read_trylock(void) { return true; }
 static inline void lockdep_assert_cpus_held(void) { }
 static inline void cpu_hotplug_disable(void) { }
 static inline void cpu_hotplug_enable(void) { }
+static inline int remove_cpu(unsigned int cpu) { return -EPERM; }
 static inline void smp_shutdown_nonboot_cpus(unsigned int primary_cpu) { }
 #endif	/* !CONFIG_HOTPLUG_CPU */
 

base-commit: 671176b0016c80b3943cb5387312c886aba3308d
-- 
2.28.0

[PATCH v2 2/2] virt: acrn: Make remove_cpu sysfs invisible with !CONFIG_HOTPLUG_CPU

[shuo.a.liu]

From: Shuo Liu <shuo.a.liu@intel.com>

Without cpu hotplug support, vCPU cannot be removed from a Service VM.
Don't expose remove_cpu sysfs when CONFIG_HOTPLUG_CPU disabled.

Signed-off-by: Shuo Liu <shuo.a.liu@intel.com>
---
 drivers/virt/acrn/hsm.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/virt/acrn/hsm.c b/drivers/virt/acrn/hsm.c
index 1f6b7c54a1a4..6996ea6219e5 100644
--- a/drivers/virt/acrn/hsm.c
+++ b/drivers/virt/acrn/hsm.c
@@ -404,6 +404,14 @@ static ssize_t remove_cpu_store(struct device *dev,
 }
 static DEVICE_ATTR_WO(remove_cpu);
 
+static umode_t acrn_attr_visible(struct kobject *kobj, struct attribute *a, int n)
+{
+       if (a == &dev_attr_remove_cpu.attr)
+               return IS_ENABLED(CONFIG_HOTPLUG_CPU) ? a->mode : 0;
+
+       return a->mode;
+}
+
 static struct attribute *acrn_attrs[] = {
 	&dev_attr_remove_cpu.attr,
 	NULL
@@ -411,6 +419,7 @@ static struct attribute *acrn_attrs[] = {
 
 static struct attribute_group acrn_attr_group = {
 	.attrs = acrn_attrs,
+	.is_visible = acrn_attr_visible,
 };
 
 static const struct attribute_group *acrn_attr_groups[] = {
-- 
2.28.0

Re: [PATCH v2 2/2] virt: acrn: Make remove_cpu sysfs invisible with !CONFIG_HOTPLUG_CPU

[Randy Dunlap]

On 2/12/21 8:55 AM, shuo.a.liu@intel.com wrote:
> From: Shuo Liu <shuo.a.liu@intel.com>
> 
> Without cpu hotplug support, vCPU cannot be removed from a Service VM.
> Don't expose remove_cpu sysfs when CONFIG_HOTPLUG_CPU disabled.
> 
> Signed-off-by: Shuo Liu <shuo.a.liu@intel.com>

Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested

Thanks.

> ---
>  drivers/virt/acrn/hsm.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/virt/acrn/hsm.c b/drivers/virt/acrn/hsm.c
> index 1f6b7c54a1a4..6996ea6219e5 100644
> --- a/drivers/virt/acrn/hsm.c
> +++ b/drivers/virt/acrn/hsm.c
> @@ -404,6 +404,14 @@ static ssize_t remove_cpu_store(struct device *dev,
>  }
>  static DEVICE_ATTR_WO(remove_cpu);
>  
> +static umode_t acrn_attr_visible(struct kobject *kobj, struct attribute *a, int n)
> +{
> +       if (a == &dev_attr_remove_cpu.attr)
> +               return IS_ENABLED(CONFIG_HOTPLUG_CPU) ? a->mode : 0;
> +
> +       return a->mode;
> +}
> +
>  static struct attribute *acrn_attrs[] = {
>  	&dev_attr_remove_cpu.attr,
>  	NULL
> @@ -411,6 +419,7 @@ static struct attribute *acrn_attrs[] = {
>  
>  static struct attribute_group acrn_attr_group = {
>  	.attrs = acrn_attrs,
> +	.is_visible = acrn_attr_visible,
>  };
>  
>  static const struct attribute_group *acrn_attr_groups[] = {
> 


-- 
~Randy

Re: [PATCH v2 1/2] cpu/hotplug: Fix build error of using {add,remove}_cpu() with !CONFIG_SMP

[Randy Dunlap]

On 2/12/21 8:55 AM, shuo.a.liu@intel.com wrote:
> From: Shuo Liu <shuo.a.liu@intel.com>
> 
> 279dcf693ac7 ("virt: acrn: Introduce an interface for Service VM to
> control vCPU") introduced {add,remove}_cpu() usage and it hit below
> error with !CONFIG_SMP:
> 
> ../drivers/virt/acrn/hsm.c: In function ‘remove_cpu_store’:
> ../drivers/virt/acrn/hsm.c:389:3: error: implicit declaration of function ‘remove_cpu’; [-Werror=implicit-function-declaration]
>    remove_cpu(cpu);
> 
> ../drivers/virt/acrn/hsm.c:402:2: error: implicit declaration of function ‘add_cpu’; [-Werror=implicit-function-declaration]
>    add_cpu(cpu);
> 
> Add add_cpu() function prototypes with !CONFIG_SMP and remove_cpu() with
> !CONFIG_HOTPLUG_CPU for such usage.
> 
> Fixes: 279dcf693ac7 ("virt: acrn: Introduce an interface for Service VM to control vCPU")
> Reported-by: Randy Dunlap <rdunlap@infradead.org>
> Signed-off-by: Shuo Liu <shuo.a.liu@intel.com>
> ---
> I followed Greg's idea that add {add,remove}_cpu() functions prototypes.
> The v2 solution is different from the v1, so i removed Randy's Acked-by.
> Randy, please help have a look on v2.
> 
> v2:
>   - Drop the #ifdef in .c solution. Add {add,remove}_cpu() prototypes. (Suggested by Greg)
> 
>  include/linux/cpu.h | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/include/linux/cpu.h b/include/linux/cpu.h
> index 3aaa0687e8df..94a578a96202 100644
> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -108,6 +108,8 @@ static inline void cpu_maps_update_done(void)
>  {
>  }
>  
> +static inline int add_cpu(unsigned int cpu) { return 0;}
> +
>  #endif /* CONFIG_SMP */
>  extern struct bus_type cpu_subsys;
>  
> @@ -137,6 +139,7 @@ static inline int  cpus_read_trylock(void) { return true; }
>  static inline void lockdep_assert_cpus_held(void) { }
>  static inline void cpu_hotplug_disable(void) { }
>  static inline void cpu_hotplug_enable(void) { }
> +static inline int remove_cpu(unsigned int cpu) { return -EPERM; }

I would have done: return 0;

Anyway:

Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested


>  static inline void smp_shutdown_nonboot_cpus(unsigned int primary_cpu) { }
>  #endif	/* !CONFIG_HOTPLUG_CPU */

thanks.

-- 
~Randy