----- On Nov 10, 2017, at 5:32 PM, Mathieu Desnoyers [email protected] wrote:
> ----- On Nov 10, 2017, at 5:20 PM, Mathieu Desnoyers > [email protected] wrote: > >> ----- On Nov 10, 2017, at 5:02 PM, Andy Lutomirski [email protected] wrote: >> >>> On Fri, Nov 10, 2017 at 1:37 PM, Mathieu Desnoyers >>> <[email protected]> wrote: >>>> Introduce an architecture function that ensures the current CPU >>>> issues a core serializing instruction before returning to usermode. >>>> >>>> This is needed to fix an existing core serialization bug on >>>> thread migration, and also needed by the membarrier "sync_core" command. >>>> >>>> Architectures defining the sync_core_before_usermode() static inline >>>> need to define ARCH_HAS_SYNC_CORE_BEFORE_USERMODE. >>>> >>>> Signed-off-by: Mathieu Desnoyers <[email protected]> >>>> CC: Peter Zijlstra <[email protected]> >>>> CC: Andy Lutomirski <[email protected]> >>>> CC: Paul E. McKenney <[email protected]> >>>> CC: Boqun Feng <[email protected]> >>>> CC: Andrew Hunter <[email protected]> >>>> CC: Maged Michael <[email protected]> >>>> CC: Avi Kivity <[email protected]> >>>> CC: Benjamin Herrenschmidt <[email protected]> >>>> CC: Paul Mackerras <[email protected]> >>>> CC: Michael Ellerman <[email protected]> >>>> CC: Dave Watson <[email protected]> >>>> CC: Thomas Gleixner <[email protected]> >>>> CC: Ingo Molnar <[email protected]> >>>> CC: "H. Peter Anvin" <[email protected]> >>>> CC: Andrea Parri <[email protected]> >>>> CC: Russell King <[email protected]> >>>> CC: Greg Hackmann <[email protected]> >>>> CC: Will Deacon <[email protected]> >>>> CC: David Sehr <[email protected]> >>>> CC: Linus Torvalds <[email protected]> >>>> CC: [email protected] >>>> CC: [email protected] >>>> --- >>>> arch/x86/Kconfig | 1 + >>>> arch/x86/include/asm/processor.h | 10 ++++++++++ >>>> include/linux/processor.h | 6 ++++++ >>>> 3 files changed, 17 insertions(+) >>>> >>>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig >>>> index 01f78c1d40b5..54fbb8960d94 100644 >>>> --- a/arch/x86/Kconfig >>>> +++ b/arch/x86/Kconfig >>>> @@ -62,6 +62,7 @@ config X86 >>>> select ARCH_HAS_SG_CHAIN >>>> select ARCH_HAS_STRICT_KERNEL_RWX >>>> select ARCH_HAS_STRICT_MODULE_RWX >>>> + select ARCH_HAS_SYNC_CORE_BEFORE_USERMODE >>>> select ARCH_HAS_UBSAN_SANITIZE_ALL >>>> select ARCH_HAS_ZONE_DEVICE if X86_64 >>>> select ARCH_HAVE_NMI_SAFE_CMPXCHG >>>> diff --git a/arch/x86/include/asm/processor.h >>>> b/arch/x86/include/asm/processor.h >>>> index bdac19ab2488..6ce996a7c730 100644 >>>> --- a/arch/x86/include/asm/processor.h >>>> +++ b/arch/x86/include/asm/processor.h >>>> @@ -706,6 +706,16 @@ static inline void sync_core(void) >>>> #endif >>>> } >>>> >>>> +/* >>>> + * Ensure that a core serializing instruction is issued before returning >>>> + * to user-mode. x86 implements return to user-space through sysexit and >>>> + * sysretq, which are not core serializing. >>>> + */ >>>> +static inline void sync_core_before_usermode(void) >>>> +{ >>>> + sync_core(); >>>> +} >>> >>> Make this if (!in_interrupt()) sync_core(); please. We can optimize >>> it better later on. >> >> Sure, done. It will be part of the next version of that patch. > > Of course, using in_interrupt() from linux/interrupt.h from > asm/processor.h is not such a good idea (circular dependency). > > Any recommendation on where to move that static inline on x86 ? Actually, for the needs of the fix, I plan on not putting the if (!in_interrupt()) check, given that the only caller will be the scheduler, not in an interrupt context. We can always revisit this optimization-wise if we end up using in interrupt handlers in the future. Is that ok with you ? Thanks, Mathieu > > Thanks, > > Mathieu > > >> >> Thanks! >> >> Mathieu >> >> >> -- >> Mathieu Desnoyers >> EfficiOS Inc. >> http://www.efficios.com > > -- > Mathieu Desnoyers > EfficiOS Inc. > http://www.efficios.com -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
