From patchwork Tue May 22 14:02:56 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Christophe Leroy X-Patchwork-Id: 918356 Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) (using TLSv1.2 with cipher ADH-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 40qyBW35mwz9s01 for ; Wed, 23 May 2018 00:06:59 +1000 (AEST) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=c-s.fr Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 40qyBW1jcbzDqnw for ; Wed, 23 May 2018 00:06:59 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=c-s.fr X-Original-To: linuxppc-dev@lists.ozlabs.org Delivered-To: linuxppc-dev@lists.ozlabs.org Authentication-Results: lists.ozlabs.org; spf=pass (mailfrom) smtp.mailfrom=c-s.fr (client-ip=93.17.236.30; helo=pegase1.c-s.fr; envelope-from=christophe.leroy@c-s.fr; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=c-s.fr Received: from pegase1.c-s.fr (pegase1.c-s.fr [93.17.236.30]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 40qy5x0wJ8zDqgs for ; Wed, 23 May 2018 00:03:00 +1000 (AEST) Received: from localhost (mailhub1-int [192.168.12.234]) by localhost (Postfix) with ESMTP id 40qy5r4HK3z9tvrd; Tue, 22 May 2018 16:02:56 +0200 (CEST) X-Virus-Scanned: Debian amavisd-new at c-s.fr Received: from pegase1.c-s.fr ([192.168.12.234]) by localhost (pegase1.c-s.fr [192.168.12.234]) (amavisd-new, port 10024) with ESMTP id pQ3-xDwKQrHj; Tue, 22 May 2018 16:02:56 +0200 (CEST) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase1.c-s.fr (Postfix) with ESMTP id 40qy5r3mXBz9tvq8; Tue, 22 May 2018 16:02:56 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 33A588B94F; Tue, 22 May 2018 16:02:57 +0200 (CEST) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id TBNlPfB1bfJm; Tue, 22 May 2018 16:02:57 +0200 (CEST) Received: from po14934vm.idsi0.si.c-s.fr (po15451.idsi0.si.c-s.fr [172.25.231.2]) by messagerie.si.c-s.fr (Postfix) with ESMTP id AEE5E8B94E; Tue, 22 May 2018 16:02:56 +0200 (CEST) Received: by po14934vm.idsi0.si.c-s.fr (Postfix, from userid 0) id A53986F941; Tue, 22 May 2018 16:02:56 +0200 (CEST) Message-Id: In-Reply-To: <1053e5f43a2ea9a9d9abb1f45c88dffb60b9b4fc.1526995927.git.christophe.leroy@c-s.fr> References: <1053e5f43a2ea9a9d9abb1f45c88dffb60b9b4fc.1526995927.git.christophe.leroy@c-s.fr> From: Christophe Leroy Subject: [PATCH v7 2/3] powerpc/mm: Only read faulting instruction when necessary in do_page_fault() To: Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , npiggin@gmail.com Date: Tue, 22 May 2018 16:02:56 +0200 (CEST) X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.26 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Errors-To: linuxppc-dev-bounces+patchwork-incoming=ozlabs.org@lists.ozlabs.org Sender: "Linuxppc-dev" Commit a7a9dcd882a67 ("powerpc: Avoid taking a data miss on every userspace instruction miss") has shown that limiting the read of faulting instruction to likely cases improves performance. This patch goes further into this direction by limiting the read of the faulting instruction to the only cases where it is likely needed. On an MPC885, with the same benchmark app as in the commit referred above, we see a reduction of about 3900 dTLB misses (approx 3%): Before the patch: Performance counter stats for './fault 500' (10 runs): 683033312 cpu-cycles ( +- 0.03% ) 134538 dTLB-load-misses ( +- 0.03% ) 46099 iTLB-load-misses ( +- 0.02% ) 19681 faults ( +- 0.02% ) 5.389747878 seconds time elapsed ( +- 0.06% ) With the patch: Performance counter stats for './fault 500' (10 runs): 682112862 cpu-cycles ( +- 0.03% ) 130619 dTLB-load-misses ( +- 0.03% ) 46073 iTLB-load-misses ( +- 0.05% ) 19681 faults ( +- 0.01% ) 5.381342641 seconds time elapsed ( +- 0.07% ) The proper work of the huge stack expansion was tested with the following app: int main(int argc, char **argv) { char buf[1024 * 1025]; sprintf(buf, "Hello world !\n"); printf(buf); exit(0); } Signed-off-by: Christophe Leroy --- v7: Following comment from Nicholas on v6 on possibility of the page getting removed from the pagetables between the fault and the read, I have reworked the patch in order to do the get_user() in __do_page_fault() directly in order to reduce complexity compared to version v5 v6: Rebased on latest powerpc/merge branch ; Using __get_user_inatomic() instead of get_user() in order to move it inside the semaphored area. That removes all the complexity of the patch. v5: Reworked to fit after Benh do_fault improvement and rebased on top of powerpc/merge (65152902e43fef) v4: Rebased on top of powerpc/next (f718d426d7e42e) and doing access_ok() verification before __get_user_xxx() v3: Do a first try with pagefault disabled before releasing the semaphore v2: Changes 'if (cond1) if (cond2)' by 'if (cond1 && cond2)' arch/powerpc/mm/fault.c | 23 ++++++++++++++++++++--- 1 file changed, 20 insertions(+), 3 deletions(-) diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c index fcbb34431da2..dc64b8e06477 100644 --- a/arch/powerpc/mm/fault.c +++ b/arch/powerpc/mm/fault.c @@ -450,9 +450,6 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address, * can result in fault, which will cause a deadlock when called with * mmap_sem held */ - if (is_write && is_user) - get_user(inst, (unsigned int __user *)regs->nip); - if (is_user) flags |= FAULT_FLAG_USER; if (is_write) @@ -498,6 +495,26 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address, if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) return bad_area(regs, address); + if (unlikely(is_write && is_user && address + 0x100000 < vma->vm_end && + !inst)) { + unsigned int __user *nip = (unsigned int __user *)regs->nip; + + if (likely(access_ok(VERIFY_READ, nip, sizeof(inst)))) { + int res; + + pagefault_disable(); + res = __get_user_inatomic(inst, nip); + pagefault_enable(); + if (unlikely(res)) { + up_read(&mm->mmap_sem); + res = __get_user(inst, nip); + if (!res && inst) + goto retry; + return bad_area_nosemaphore(regs, address); + } + } + } + /* The stack is being expanded, check if it's valid */ if (unlikely(bad_stack_expansion(regs, address, vma, inst))) return bad_area(regs, address);