Re: [kvm-unit-tests PATCH 3/4] arm/arm64: Track whether thread_info has been initialized

[Alexandru Elisei <alexandru.elisei@arm.com>]

Hi Nikos,

On 3/19/21 12:24 PM, Nikos Nikoleris wrote:
> Introduce a new flag in the thread_info to track whether a thread_info
> struct is initialized yet or not.

There's no explanation why this is needed. The flag checked only by is_user(), and
before thread_info is initialized, flags is zero, so is_user() would return false,
right? Or am I missing something?

Thanks,

Alex

>
> Signed-off-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
> ---
>  lib/arm/asm/thread_info.h | 1 +
>  lib/arm/processor.c       | 5 +++--
>  lib/arm64/processor.c     | 5 +++--
>  3 files changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/lib/arm/asm/thread_info.h b/lib/arm/asm/thread_info.h
> index eaa7258..926c2a3 100644
> --- a/lib/arm/asm/thread_info.h
> +++ b/lib/arm/asm/thread_info.h
> @@ -45,6 +45,7 @@ static inline void *thread_stack_alloc(void)
>  }
>  
>  #define TIF_USER_MODE		(1U << 0)
> +#define TIF_VALID		(1U << 1)
>  
>  struct thread_info {
>  	int cpu;
> diff --git a/lib/arm/processor.c b/lib/arm/processor.c
> index a2d39a4..702fbc3 100644
> --- a/lib/arm/processor.c
> +++ b/lib/arm/processor.c
> @@ -119,7 +119,7 @@ void thread_info_init(struct thread_info *ti, unsigned int flags)
>  {
>  	memset(ti, 0, sizeof(struct thread_info));
>  	ti->cpu = mpidr_to_cpu(get_mpidr());
> -	ti->flags = flags;
> +	ti->flags = flags | TIF_VALID;
>  }
>  
>  void start_usr(void (*func)(void *arg), void *arg, unsigned long sp_usr)
> @@ -143,7 +143,8 @@ void start_usr(void (*func)(void *arg), void *arg, unsigned long sp_usr)
>  
>  bool is_user(void)
>  {
> -	return current_thread_info()->flags & TIF_USER_MODE;
> +	struct thread_info *ti = current_thread_info();
> +	return (ti->flags & TIF_VALID) && (ti->flags & TIF_USER_MODE);
>  }
>  
>  bool __mmu_enabled(void)
> diff --git a/lib/arm64/processor.c b/lib/arm64/processor.c
> index ef55862..231d71e 100644
> --- a/lib/arm64/processor.c
> +++ b/lib/arm64/processor.c
> @@ -227,7 +227,7 @@ static void __thread_info_init(struct thread_info *ti, unsigned int flags)
>  {
>  	memset(ti, 0, sizeof(struct thread_info));
>  	ti->cpu = mpidr_to_cpu(get_mpidr());
> -	ti->flags = flags;
> +	ti->flags = flags | TIF_VALID;
>  }
>  
>  void thread_info_init(struct thread_info *ti, unsigned int flags)
> @@ -255,7 +255,8 @@ void start_usr(void (*func)(void *arg), void *arg, unsigned long sp_usr)
>  
>  bool is_user(void)
>  {
> -	return current_thread_info()->flags & TIF_USER_MODE;
> +	struct thread_info *ti = current_thread_info();
> +	return (ti->flags & TIF_VALID) && (ti->flags & TIF_USER_MODE);
>  }
>  
>  bool __mmu_enabled(void)