On 28/05/2020 21:19, Peter Zijlstra wrote: > --- a/arch/x86/include/asm/debugreg.h > +++ b/arch/x86/include/asm/debugreg.h > @@ -113,6 +113,31 @@ static inline void debug_stack_usage_inc > static inline void debug_stack_usage_dec(void) { } > #endif /* X86_64 */ > > +static __always_inline void local_db_save(unsigned long *dr7) > +{ > + get_debugreg(*dr7, 7); > + if (*dr7) > + set_debugreg(0, 7);
%dr7 has an architecturally stuck bit in it. You want *dr7 != 0x400 to avoid writing 0 unconditionally. Also, API wise, wouldn't it be nicer to write "dr7 = local_db_save()" rather than having a void function returning a single long via pointer? ~Andrew