Re: [PATCH v9 05/26] x86/fpu/xstate: Add new variables to indicate dynamic XSTATE buffer size

Borislav Petkov
2021-08-12T15:02:47Z

On Fri, Jul 30, 2021 at 07:59:36AM -0700, Chang S. Bae wrote:
> @@ -167,8 +158,10 @@ static void __init fpu__init_task_struct_size(void)
> /*
> * Add back the dynamically-calculated register state
> * size.
> + *
> + * Use the minimum size as embedded to task_struct.

embedded in...

> diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
> index 74e608c6ad6c..12caf1a56ce0 100644
> --- a/arch/x86/kernel/fpu/xstate.c
> +++ b/arch/x86/kernel/fpu/xstate.c
> @@ -77,12 +77,51 @@ static unsigned int xstate_comp_offsets[XFEATURE_MAX] __ro_after_init =
> static unsigned int xstate_supervisor_only_offsets[XFEATURE_MAX] __ro_after_init =
> { [ 0 ... XFEATURE_MAX - 1] = -1};
>
> -/*
> - * The XSAVE area of kernel can be in standard or compacted format;
> - * it is always in standard format for user mode. This is the user
> - * mode standard format size used for signal and ptrace frames.
> +/**
> + * struct fpu_xstate_buffer_config - xstate buffer configuration
> + * @max_size: The CPUID-enumerated all-feature "maximum" size
> + * for xstate per-task buffer.
> + * @min_size: The size to fit into the statically-allocated
> + * buffer. With dynamic states, this buffer no longer
> + * contains all the enabled state components.
> + * @user_size: The size of user-space buffer for signal and
> + * ptrace frames, in the non-compacted format.
> */
> -unsigned int fpu_user_xstate_size __ro_after_init;
> +struct fpu_xstate_buffer_config {
> + unsigned int min_size, max_size;
> + unsigned int user_size;
> +};
> +
> +static struct fpu_xstate_buffer_config buffer_config __ro_after_init;

I know I had asked for the accessors below but if this is going to be
read-only after init and is not going to change for duration of the
system lifetime, then you don't really need those accessors.

I.e., you can do

struct fpu_xstate_buffer_config {
unsigned int min_size, max_size;
unsigned int user_size;
};

static struct fpu_xstate_buffer_config fpu_buf_cfg __ro_after_init;

and then access those values through fpu_buf_cfg.<value>

Thx.

> +
> +unsigned int get_xstate_config(enum xstate_config cfg)
> +{
> + switch (cfg) {
> + case XSTATE_MIN_SIZE:
> + return buffer_config.min_size;
> + case XSTATE_MAX_SIZE:
> + return buffer_config.max_size;
> + case XSTATE_USER_SIZE:
> + return buffer_config.user_size;
> + default:
> + return 0;
> + }
> +}
> +EXPORT_SYMBOL_GPL(get_xstate_config);
> +
> +void set_xstate_config(enum xstate_config cfg, unsigned int value)
> +{
> + switch (cfg) {
> + case XSTATE_MIN_SIZE:
> + buffer_config.min_size = value;
> + break;
> + case XSTATE_MAX_SIZE:
> + buffer_config.max_size = value;
> + break;
> + case XSTATE_USER_SIZE:
> + buffer_config.user_size = value;
> + }
> +}

--
Regards/Gruss,
Boris.