From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:41652 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S968498AbeCSSJs (ORCPT ); Mon, 19 Mar 2018 14:09:48 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Anton Blanchard , Michael Ellerman , Sasha Levin Subject: [PATCH 3.18 26/68] powerpc: Avoid taking a data miss on every userspace instruction miss Date: Mon, 19 Mar 2018 19:06:04 +0100 Message-Id: <20180319171831.528802054@linuxfoundation.org> In-Reply-To: <20180319171827.899658615@linuxfoundation.org> References: <20180319171827.899658615@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: stable-owner@vger.kernel.org List-ID: 3.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Anton Blanchard [ Upstream commit a7a9dcd882a67b68568868b988289fce5ffd8419 ] Early on in do_page_fault() we call store_updates_sp(), regardless of the type of exception. For an instruction miss this doesn't make sense, because we only use this information to detect if a data miss is the result of a stack expansion instruction or not. Worse still, it results in a data miss within every userspace instruction miss handler, because we try and load the very instruction we are about to install a pte for! A simple exec microbenchmark runs 6% faster on POWER8 with this fix: #include #include #include int main(int argc, char *argv[]) { unsigned long left = atol(argv[1]); char leftstr[16]; if (left-- == 0) return 0; sprintf(leftstr, "%ld", left); execlp(argv[0], argv[0], leftstr, NULL); perror("exec failed\n"); return 0; } Pass the number of iterations on the command line (eg 10000) and time how long it takes to execute. Signed-off-by: Anton Blanchard Signed-off-by: Michael Ellerman Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- arch/powerpc/mm/fault.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/arch/powerpc/mm/fault.c +++ b/arch/powerpc/mm/fault.c @@ -294,7 +294,7 @@ int __kprobes do_page_fault(struct pt_re * can result in fault, which will cause a deadlock when called with * mmap_sem held */ - if (user_mode(regs)) + if (!is_exec && user_mode(regs)) store_update_sp = store_updates_sp(regs); if (user_mode(regs))