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Commit 5b073430 authored by Ingo Molnar's avatar Ingo Molnar
Browse files

x86/fpu: Introduce cpu_has_xfeatures(xfeatures_mask, feature_name) 



A lot of FPU using driver code is querying complex CPU features to be
able to figure out whether a given set of xstate features is supported
by the CPU or not.

Introduce a simplified API function that can be used on any CPU type
to get this information. Also add an error string return pointer,
so that the driver can print a meaningful error message with a
standardized feature name.

Also mark xfeatures_mask as __read_only.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 62784854

arch/x86/include/asm/fpu/api.h

+9 −0
Original line number Diff line number Diff line
@@ -36,4 +36,13 @@ extern bool irq_fpu_usable(void); 
extern int  irq_ts_save(void);

extern void irq_ts_restore(int TS_state);



/*

 * Query the presence of one or more xfeatures. Works on any legacy CPU as well.

 *

 * If 'feature_name' is set then put a human-readable description of

 * the feature there as well - this can be used to print error (or success)

 * messages.

 */

extern int cpu_has_xfeatures(u64 xfeatures_mask, const char **feature_name);



#endif /* _ASM_X86_FPU_API_H */

arch/x86/kernel/fpu/xstate.c

+52 −1
Original line number Diff line number Diff line
@@ -11,10 +11,23 @@ 
#include <asm/tlbflush.h>

#include <asm/xcr.h>



static const char *xfeature_names[] =

{

	"x87 floating point registers"	,

	"SSE registers"			,

	"AVX registers"			,

	"MPX bounds registers"		,

	"MPX CSR"			,

	"AVX-512 opmask"		,

	"AVX-512 Hi256"			,

	"AVX-512 ZMM_Hi256"		,

	"unknown xstate feature"	,

};



/*

 * Mask of xstate features supported by the CPU and the kernel:

 */

u64 xfeatures_mask;

u64 xfeatures_mask __read_mostly;



/*

 * Represents init state for the supported extended state.
@@ -28,6 +41,44 @@ static unsigned int xstate_comp_offsets[sizeof(xfeatures_mask)*8]; 
/* The number of supported xfeatures in xfeatures_mask: */

static unsigned int xfeatures_nr;



/*

 * Return whether the system supports a given xfeature.

 *

 * Also return the name of the (most advanced) feature that the caller requested:

 */

int cpu_has_xfeatures(u64 xfeatures_needed, const char **feature_name)

{

	u64 xfeatures_missing = xfeatures_needed & ~xfeatures_mask;



	if (unlikely(feature_name)) {

		long xfeature_idx, max_idx;

		u64 xfeatures_print;

		/*

		 * So we use FLS here to be able to print the most advanced

		 * feature that was requested but is missing. So if a driver

		 * asks about "XSTATE_SSE | XSTATE_YMM" we'll print the

		 * missing AVX feature - this is the most informative message

		 * to users:

		 */

		if (xfeatures_missing)

			xfeatures_print = xfeatures_missing;

		else

			xfeatures_print = xfeatures_needed;



		xfeature_idx = fls64(xfeatures_print)-1;

		max_idx = ARRAY_SIZE(xfeature_names)-1;

		xfeature_idx = min(xfeature_idx, max_idx);



		*feature_name = xfeature_names[xfeature_idx];

	}



	if (xfeatures_missing)

		return 0;



	return 1;

}

EXPORT_SYMBOL_GPL(cpu_has_xfeatures);



/*

 * When executing XSAVEOPT (optimized XSAVE), if a processor implementation

 * detects that an FPU state component is still (or is again) in its