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arm64: read the SME2 vector length only after the FEAT_SME2 test #6153

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arm64: read the SME2 vector length only after the FEAT_SME2 test #6153

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9 changes: 8 additions & 1 deletion kernel/arm64/sme2_gemm_detect.h
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Original file line number Diff line number Diff line change
Expand Up @@ -41,6 +41,13 @@ THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#include <sys/auxv.h>
#endif

/* Streaming vector length in fp32 lanes; volatile asm and noinline keep RDSVL behind the FEAT_SME2 test. */
static __attribute__((noinline)) int s2_svl_lanes(void) {
unsigned long svl;
__asm__ volatile("rdsvl %0, #1" : "=r"(svl));
return (int)(svl / 4);
}

/* SME2 with a 512-bit streaming vector length (the kernels assume 16 fp32 lanes). */
static inline int s2_usable(void) {
static int ok = -1;
Expand All @@ -53,7 +60,7 @@ static inline int s2_usable(void) {
#elif defined(__linux__)
sme2 = (getauxval(AT_HWCAP2) & (1UL << 37)) != 0; /* HWCAP2_SME2 */
#endif
ok = sme2 && svcntsw() == 16;
ok = sme2 ? s2_svl_lanes() == 16 : 0;
}
return ok;
}
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