From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mathieu Desnoyers Subject: Re: [PATCH for 4.16 07/11] x86: Implement sync_core_before_usermode (v3) Date: Wed, 17 Jan 2018 18:10:36 +0000 (UTC) Message-ID: <712464074.4666.1516212636860.JavaMail.zimbra@efficios.com> References: <20180117165458.13330-1-mathieu.desnoyers@efficios.com> <20180117165458.13330-8-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-arch-owner@vger.kernel.org To: Andy Lutomirski Cc: Ingo Molnar , Peter Zijlstra , Thomas Gleixner , linux-kernel , linux-api , "Paul E. McKenney" , Boqun Feng , Andrew Hunter , maged michael , Avi Kivity , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Dave Watson , "H. Peter Anvin" , Andrea Parri , "Russell King, ARM Linux" , Greg Hackmann , Will Deacon , David List-Id: linux-api@vger.kernel.org ----- On Jan 17, 2018, at 12:53 PM, Andy Lutomirski luto@kernel.org wrote: > On Wed, Jan 17, 2018 at 8:54 AM, Mathieu Desnoyers > wrote: >> Ensure that a core serializing instruction is issued before returning to >> user-mode. x86 implements return to user-space through sysexit, sysrel, >> and sysretq, which are not core serializing. >> >> Signed-off-by: Mathieu Desnoyers >> Reviewed-by: Thomas Gleixner >> 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: 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@kernel.org >> CC: linux-arch@vger.kernel.org >> --- >> Changes since v1: >> - Fix prototype of sync_core_before_usermode in generic code (missing >> return type). >> - Add linux/processor.h include to sched/core.c. >> - Add ARCH_HAS_SYNC_CORE_BEFORE_USERMODE to init/Kconfig. >> - Fix linux/processor.h ifdef to target >> CONFIG_ARCH_HAS_SYNC_CORE_BEFORE_USERMODE rather than >> ARCH_HAS_SYNC_CORE_BEFORE_USERMODE. >> - Move empty static inline in processor.h to generic patch. >> --- >> arch/x86/Kconfig | 1 + >> arch/x86/include/asm/processor.h | 10 ++++++++++ >> 2 files changed, 11 insertions(+) >> >> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig >> index 20da391b5f32..0b44c8dd0e95 100644 >> --- a/arch/x86/Kconfig >> +++ b/arch/x86/Kconfig >> @@ -61,6 +61,7 @@ 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 d3a67fba200a..3257d34dbb40 100644 >> --- a/arch/x86/include/asm/processor.h >> +++ b/arch/x86/include/asm/processor.h >> @@ -722,6 +722,16 @@ 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, >> + * sysrel, and sysretq, which are not core serializing. >> + */ >> +static inline void sync_core_before_usermode(void) >> +{ > > /* With PTI, we unconditionally serialize before running user code. */ > if (static_cpu_has(X86_FEATURE_PTI)) > return; One issue I'm facing with this change is header dependency: sync_core_before_usermode() is currently implemented in arch/x86/include/asm/processor.h, but arch/x86/include/asm/cpufeature.h is needed for static_cpu_has, and it happens to include asm/processor.h. I'm facing a similar issue for adding a (in_irq() || in_nmi()) check. Should we move sync_core_before_usermode() to a different header, and if so, any suggestion ? Thanks, Mathieu > >> + sync_core(); >> +} > > --Andy -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com