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McKenney" , Michal Clapinski , Andrei Vagin , Shuah Khan , Aniket Gattani , linux-kselftest@vger.kernel.org, Andrew Morton , Chris Gellermann , Bala-Vignesh-Reddy , Wei Yang , Thomas Gleixner , Huacai Chen , WANG Xuerui , loongarch@lists.linux.dev, "James E.J. Bottomley" , Helge Deller , John David Anglin , linux-parisc@vger.kernel.org, Jonathan Corbet , Shuah Khan , Randy Dunlap , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Guo Ren , linux-doc@vger.kernel.org, linux-riscv@lists.infradead.org, linux-csky@vger.kernel.org, Jonas Bonn , Stefan Kristiansson , Stafford Horne , linux-openrisc@vger.kernel.org, Yoshinori Sato , Rich Felker , John Paul Adrian Glaubitz , linux-sh@vger.kernel.org, Chris Zankel , Max Filippov , linux-arch@vger.kernel.org, Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Catalin Marinas , Will Deacon , Mark Rutland , linux-arm-kernel@lists.infradead.org, Andy Lutomirski , Alan Stern , Andrea Parri , Boqun Feng , Nicholas Piggin , David Howells , Jade Alglave , Luc Maranget , Akira Yokosawa , Daniel Lustig , Joel Fernandes , lkmm@lists.linux.dev, bpf@vger.kernel.org, Naveen N Rao , "David S. Miller" , Masami Hiramatsu , linux-trace-kernel@vger.kernel.org Subject: [RFC PATCH 12/16] x86/entry: Remove stale membarrier sync core comments Date: Fri, 13 Nov 2026 08:18:59 -0500 Message-Id: <20261113131903.157186-13-mathieu.desnoyers@efficios.com> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20261113131903.157186-1-mathieu.desnoyers@efficios.com> References: <20261113131903.157186-1-mathieu.desnoyers@efficios.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Two comments state that the membarrier sync core command relies on the IRET which returns from the IPI handler. This is no longer true since commit a493d1ca1a03 ("x86/membarrier: Get rid of a dubious optimization"): sync_core_before_usermode() serializes the core in the IPI handler. Remove both comments. The comment of sync_core_before_usermode() lists the instructions which return to user-space without serializing the core. Fix a typo in it ("sysrel") and add ERETU, which FRED uses. Signed-off-by: Mathieu Desnoyers --- arch/x86/entry/entry_32.S | 5 ----- arch/x86/entry/entry_64.S | 4 ---- arch/x86/include/asm/sync_core.h | 2 +- 3 files changed, 1 insertion(+), 10 deletions(-) diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index 92c0b4a94e0a..d47bb08afb24 100644 --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -954,11 +954,6 @@ restore_all_switch_stack: RESTORE_REGS pop=4 # skip orig_eax/error_code CLEAR_CPU_BUFFERS .Lirq_return: - /* - * ARCH_HAS_MEMBARRIER_SYNC_CORE rely on IRET core serialization - * when returning from IPI handler and when returning from - * scheduler to user-space. - */ iret .Lasm_iret_error: diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index 253f0a585927..b8661064232c 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -626,10 +626,6 @@ SYM_INNER_LABEL(restore_regs_and_return_to_kernel, SYM_L_GLOBAL) #endif POP_REGS addq $8, %rsp /* skip regs->orig_ax */ - /* - * ARCH_HAS_MEMBARRIER_SYNC_CORE rely on IRET core serialization - * when returning from IPI handler. - */ #ifdef CONFIG_XEN_PV SYM_INNER_LABEL(early_xen_iret_patch, SYM_L_GLOBAL) ANNOTATE_NOENDBR diff --git a/arch/x86/include/asm/sync_core.h b/arch/x86/include/asm/sync_core.h index df22113db9cd..0ab91f7e2020 100644 --- a/arch/x86/include/asm/sync_core.h +++ b/arch/x86/include/asm/sync_core.h @@ -91,7 +91,7 @@ static __always_inline void sync_core(void) /* * 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. + * sysretl, sysretq and eretu, which are not core serializing. */ static inline void sync_core_before_usermode(void) { -- 2.47.3