Re: [PATCH v10 05/28] x86/fpu/xstate: Add a new variable to indicate dynamic user states

[Thomas Gleixner]

On Wed, Aug 25 2021 at 08:53, Chang S. Bae wrote:
> +/*
> + * This represents user xstates, a subset of xfeatures_mask_all, saved in a
> + * dynamic kernel XSAVE buffer.
> + */
> +u64 xfeatures_mask_user_dynamic __ro_after_init;
> +
>  static unsigned int xstate_offsets[XFEATURE_MAX] __ro_after_init =
>  	{ [ 0 ... XFEATURE_MAX - 1] = -1};
>  static unsigned int xstate_sizes[XFEATURE_MAX] __ro_after_init =
> @@ -709,6 +715,7 @@ static int __init init_xstate_size(void)
>  static void fpu__init_disable_system_xstate(void)
>  {
>  	xfeatures_mask_all = 0;
> +	xfeatures_mask_user_dynamic = 0;

It's zero at boot already, isn't it?

>  	cr4_clear_bits(X86_CR4_OSXSAVE);
>  	setup_clear_cpu_cap(X86_FEATURE_XSAVE);
>  }
> @@ -780,6 +787,8 @@ void __init fpu__init_system_xstate(void)
>  
>  	/* Store it for paranoia check at the end */
>  	xfeatures = xfeatures_mask_all;
> +	/* Do not support the dynamically allocated buffer yet. */
> +	xfeatures_mask_user_dynamic = 0;
>  
>  	/* Enable xstate instructions to be able to continue with initialization: */
>  	fpu__init_cpu_xstate();