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SubjectRe: [PATCH 1/6] x86/fpu/xstate: Fix small issues before adding supervisor xstates
On Wed, Sep 25, 2019 at 08:10:17AM -0700, Yu-cheng Yu wrote:
> In response to earlier comments, fix small issues before introducing XSAVES
> supervisor states:
> - Add spaces around '*'.
> - Fix comments of xfeature_is_supervisor().
> - Replace ((u64)1 << 63) with XCOMP_BV_COMPACTED_FORMAT.
>
> No functional changes from this patch.
>
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
> Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
> Reviewed-by: Tony Luck <tony.luck@intel.com>
> ---
> arch/x86/kernel/fpu/xstate.c | 15 ++++++---------
> 1 file changed, 6 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
> index e5cb67d67c03..b793fc2156b9 100644
> --- a/arch/x86/kernel/fpu/xstate.c
> +++ b/arch/x86/kernel/fpu/xstate.c
> @@ -60,7 +60,7 @@ u64 xfeatures_mask __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) * 8];
>
> /*
> * The XSAVE area of kernel can be in standard or compacted format;
> @@ -110,12 +110,8 @@ EXPORT_SYMBOL_GPL(cpu_has_xfeatures);
> static int xfeature_is_supervisor(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
> - * state component, ECX[0] returns 1.
> + * Extended State Enumeration Sub-leaves (EAX = 0DH, ECX = n, n > 1)
> + * returns ECX[0] set to (1) for a supervisor state.

"... and cleared (0) for a user state."

I believe it is is clearer this way.

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

Since you're touching this function: make it return bool as it is used
in boolean context only and have it return simply:

return ecx & 1;

Thx.

--
Regards/Gruss,
Boris.

https://people.kernel.org/tglx/notes-about-netiquette

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