From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mathieu Desnoyers Subject: Re: [RFC PATCH for 4.15 05/10] x86: Introduce sync_core_before_usermode Date: Fri, 10 Nov 2017 22:20:30 +0000 (UTC) Message-ID: <1007217384.13056.1510352430448.JavaMail.zimbra@efficios.com> References: <20171110213717.12457-1-mathieu.desnoyers@efficios.com> <20171110213717.12457-6-mathieu.desnoyers@efficios.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Andy Lutomirski Cc: Boqun Feng , Peter Zijlstra , "Paul E. McKenney" , linux-kernel , linux-api , Andrew Hunter , maged michael , Avi Kivity , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Dave Watson , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Andrea Parri , "Russell King, ARM Linux" , Greg Hackmann , Will Deacon , David List-Id: linux-api@vger.kernel.org ----- On Nov 10, 2017, at 5:02 PM, Andy Lutomirski luto-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org wrote: > On Fri, Nov 10, 2017 at 1:37 PM, Mathieu Desnoyers > 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 >> CC: Peter Zijlstra >> CC: Andy Lutomirski >> CC: Paul E. McKenney >> CC: Boqun Feng >> CC: Andrew Hunter >> CC: Maged Michael >> CC: Avi Kivity >> CC: Benjamin Herrenschmidt >> CC: Paul Mackerras >> CC: Michael Ellerman >> CC: Dave Watson >> CC: Thomas Gleixner >> CC: Ingo Molnar >> CC: "H. Peter Anvin" >> CC: Andrea Parri >> CC: Russell King >> CC: Greg Hackmann >> CC: Will Deacon >> CC: David Sehr >> CC: Linus Torvalds >> CC: x86-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org >> CC: linux-arch-u79uwXL29TY76Z2rM5mHXA@public.gmane.org >> --- >> 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. Thanks! Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com