diff options
| -rw-r--r-- | arch/s390/include/asm/preempt.h | 20 |
1 files changed, 18 insertions, 2 deletions
diff --git a/arch/s390/include/asm/preempt.h b/arch/s390/include/asm/preempt.h index 6ccd033acfe5..6d6a28bee4e7 100644 --- a/arch/s390/include/asm/preempt.h +++ b/arch/s390/include/asm/preempt.h @@ -8,7 +8,10 @@ #include <asm/cmpxchg.h> #include <asm/march.h> -/* We use the MSB mostly because its available */ +/* + * Use MSB so it is possible to read preempt_count with LLGT which + * reads the least significant 31 bits with a single instruction. + */ #define PREEMPT_NEED_RESCHED 0x80000000 /* @@ -23,7 +26,20 @@ */ static __always_inline int preempt_count(void) { - return READ_ONCE(get_lowcore()->preempt_count) & ~PREEMPT_NEED_RESCHED; + unsigned long lc_preempt, count; + + BUILD_BUG_ON(sizeof_field(struct lowcore, preempt_count) != sizeof(int)); + lc_preempt = offsetof(struct lowcore, preempt_count); + /* READ_ONCE(get_lowcore()->preempt_count) & ~PREEMPT_NEED_RESCHED */ + asm_inline( + ALTERNATIVE("llgt %[count],%[offzero](%%r0)\n", + "llgt %[count],%[offalt](%%r0)\n", + ALT_FEATURE(MFEATURE_LOWCORE)) + : [count] "=d" (count) + : [offzero] "i" (lc_preempt), + [offalt] "i" (lc_preempt + LOWCORE_ALT_ADDRESS), + "m" (((struct lowcore *)0)->preempt_count)); + return count; } static __always_inline void preempt_count_set(int pc) |