Re: [PATCH v9 07/26] x86/fpu/xstate: Convert the struct fpu 'state' field to a pointer

[Borislav Petkov]

On Fri, Jul 30, 2021 at 07:59:38AM -0700, Chang S. Bae wrote:
> diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
> index f5a38a5f3ae1..c7826708f27f 100644
> --- a/arch/x86/include/asm/fpu/types.h
> +++ b/arch/x86/include/asm/fpu/types.h
> @@ -339,13 +339,30 @@ struct fpu {
>  	/*
>  	 * @state:
>  	 *
> -	 * In-memory copy of all FPU registers that we save/restore
> -	 * over context switches. If the task is using the FPU then
> -	 * the registers in the FPU are more recent than this state
> -	 * copy. If the task context-switches away then they get
> -	 * saved here and represent the FPU state.
> +	 * A pointer to indicate the in-memory copy of all FPU registers
> +	 * that are saved/restored over context switches.
> +	 *
> +	 * Initially @state points to @__default_state. When dynamic states
> +	 * get used, a memory is allocated for the larger state copy and
> +	 * @state is updated to point to it. Then, the state in ->state
> +	 * supersedes and invalidates the state in @__default_state.
> +	 *
> +	 * In general, if the task is using the FPU then the registers in
> +	 * the FPU are more recent than the state copy. If the task
> +	 * context-switches away then they get saved in ->state and
> +	 * represent the FPU state.
> +	 */
> +	union fpregs_state		*state;
> +
> +	/*
> +	 * @__default_state:
> +	 *
> +	 * Initial in-memory copy of all FPU registers that saved/restored
> +	 * over context switches. When the task is switched to dynamic
> +	 * states, this copy is replaced with the new in-memory copy in
> +	 * ->state.
>  	 */
> -	union fpregs_state		state;
> +	union fpregs_state		__default_state;
>  	/*
>  	 * WARNING: 'state' is dynamically-sized.  Do not put
		    ^^^^^^

that needs to be __default_state as it is which is dynamically-sized.

-- 
Regards/Gruss,
    Boris.

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