Re: [PATCH v5 02/27] x86/fpu/xstate: Change names to separate XSAVES system and user states

Borislav Petkov
2018-10-15T17:03:20Z

On Thu, Oct 11, 2018 at 08:14:58AM -0700, Yu-cheng Yu wrote:
> Control Flow Enforcement (CET) MSRs are XSAVES system/supervisor
> states. To support CET, we introduce XSAVES system states first.
>
> XSAVES is a "supervisor" instruction and, comparing to XSAVE, saves
> additional "supervisor" states that can be modified only from CPL 0.
> However, these states are per-task and not kernel's own. Rename
> "supervisor" states to "system" states to clearly separate them from
> "user" states.
>
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
> ---
> arch/x86/include/asm/fpu/internal.h | 4 +-
> arch/x86/include/asm/fpu/xstate.h | 20 +++----
> arch/x86/kernel/fpu/core.c | 4 +-
> arch/x86/kernel/fpu/init.c | 2 +-
> arch/x86/kernel/fpu/signal.c | 6 +--
> arch/x86/kernel/fpu/xstate.c | 82 ++++++++++++++---------------
> 6 files changed, 57 insertions(+), 61 deletions(-)

...

> diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
> index 87a57b7642d3..e7cbaed12ef1 100644
> --- a/arch/x86/kernel/fpu/xstate.c
> +++ b/arch/x86/kernel/fpu/xstate.c
> @@ -51,13 +51,14 @@ static short xsave_cpuid_features[] __initdata = {
> };
>
> /*
> - * Mask of xstate features supported by the CPU and the kernel:
> + * Mask of supported 'user' xstate features derived from boot_cpu_has() and
> + * SUPPORTED_XFEATURES_MASK.

<--- This comment here looks like a good place to put some blurb about
user and system states, what they are, what the distinction is and so
on.

> */
> -u64 xfeatures_mask __read_mostly;
> +u64 xfeatures_mask_user __read_mostly;
>
> static unsigned int xstate_offsets[XFEATURE_MAX] = { [ 0 ... XFEATURE_MAX - 1] = -1};
> static unsigned int xstate_sizes[XFEATURE_MAX] = { [ 0 ... XFEATURE_MAX - 1] = -1};
> -static unsigned int xstate_comp_offsets[sizeof(xfeatures_mask)*8];
> +static unsigned int xstate_comp_offsets[sizeof(xfeatures_mask_user)*8];
>
> /*
> * The XSAVE area of kernel can be in standard or compacted format;
> @@ -82,7 +83,7 @@ void fpu__xstate_clear_all_cpu_caps(void)
> */
> int cpu_has_xfeatures(u64 xfeatures_needed, const char **feature_name)
> {
> - u64 xfeatures_missing = xfeatures_needed & ~xfeatures_mask;
> + u64 xfeatures_missing = xfeatures_needed & ~xfeatures_mask_user;
>
> if (unlikely(feature_name)) {
> long xfeature_idx, max_idx;
> @@ -113,14 +114,11 @@ int cpu_has_xfeatures(u64 xfeatures_needed, const char **feature_name)
> }
> EXPORT_SYMBOL_GPL(cpu_has_xfeatures);
>
> -static int xfeature_is_supervisor(int xfeature_nr)
> +static int xfeature_is_system(int xfeature_nr)
> {
> /*
> - * We currently do not support supervisor states, but if
> - * we did, we could find out like this.
> - *
> * SDM says: If state component 'i' is a user state component,
> - * ECX[0] return 0; if state component i is a supervisor
> + * ECX[0] return 0; if state component i is a system

is 0

> * state component, ECX[0] returns 1.

is 1.

> */
> u32 eax, ebx, ecx, edx;

...

> @@ -242,7 +238,7 @@ void fpu__init_cpu_xstate(void)
> */
> static int xfeature_enabled(enum xfeature xfeature)
> {
> - return !!(xfeatures_mask & (1UL << xfeature));
> + return !!(xfeatures_mask_user & BIT_ULL(xfeature));
> }
>
> /*
> @@ -272,7 +268,7 @@ static void __init setup_xstate_features(void)
> cpuid_count(XSTATE_CPUID, i, &eax, &ebx, &ecx, &edx);
>
> /*
> - * If an xfeature is supervisor state, the offset
> + * If an xfeature is system state, the offset

is a system state, ...

> * in EBX is invalid. We leave it to -1.
> */
> if (xfeature_is_user(i))

--
Regards/Gruss,
Boris.

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