Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754434AbdDMOxp (ORCPT ); Thu, 13 Apr 2017 10:53:45 -0400 Received: from pegase1.c-s.fr ([93.17.236.30]:59464 "EHLO pegase1.c-s.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753737AbdDMOxo (ORCPT ); Thu, 13 Apr 2017 10:53:44 -0400 From: Christophe Leroy Subject: [PATCH] powerpc/mm: some cleanup of do_page_fault() To: Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Scott Wood Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Message-Id: <20170413145342.40ED56E667@localhost.localdomain> Date: Thu, 13 Apr 2017 16:53:42 +0200 (CEST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5487 Lines: 155 This patch is a bunch of small cleanups of the do_page_fault() function: 1/ Function store_updates_sp() checks whether the faulting instruction is a store updating r1. Therefore we can limit its calls to stores exceptions 2/ Only the get_user() in store_updates_sp() has to be done outside the mm semaphore. All the comparison can be done within the semaphore, so only when really needed. 3/ As we got a DSI exception, the address pointed by regs->nip is obviously valid, otherwise we would have had a instruction exception. So __get_user() can be used instead of get_user() 4/ Replaced one duplicate 'trap == 0x400' by 'is_exec' 5/ Created a 'is_user = user_mode(regs)' and replaced all 'user_mode(regs)'. Analysis of the assembly code shows that when using user_mode(regs), at least the 'andi. r7,r8,16384' is redone several times, and also the 'lwz r8,132(r31)' at times. With the new form, the 'is_user' is mapped to cr4, then all further use of is_user results in just things like 'beq cr4,218 ' 6/ The 8xx has a dedicated exception for breakpoints, that directly calls do_break() 7/ stdu and stdux only exist on PPC64, so no need to check for them on PPC32 With this patch, on PPC8xx the size of do_page_fault() is reduced by 12% (from 1420 bytes to 1248 bytes) Signed-off-by: Christophe Leroy --- arch/powerpc/mm/fault.c | 34 ++++++++++++++++++---------------- 1 file changed, 18 insertions(+), 16 deletions(-) diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c index 3a7d580fdc59..5aa43268baca 100644 --- a/arch/powerpc/mm/fault.c +++ b/arch/powerpc/mm/fault.c @@ -73,12 +73,8 @@ static inline int notify_page_fault(struct pt_regs *regs) * Check whether the instruction at regs->nip is a store using * an update addressing form which will update r1. */ -static int store_updates_sp(struct pt_regs *regs) +static int store_updates_sp(unsigned int inst) { - unsigned int inst; - - if (get_user(inst, (unsigned int __user *)regs->nip)) - return 0; /* check for 1 in the rA field */ if (((inst >> 16) & 0x1f) != 1) return 0; @@ -90,12 +86,16 @@ static int store_updates_sp(struct pt_regs *regs) case 53: /* stfsu */ case 55: /* stfdu */ return 1; +#ifdef CONFIG_PPC64 case 62: /* std or stdu */ return (inst & 3) == 1; +#endif case 31: /* check minor opcode */ switch ((inst >> 1) & 0x3ff) { +#ifdef CONFIG_PPC64 case 181: /* stdux */ +#endif case 183: /* stwux */ case 247: /* stbux */ case 439: /* sthux */ @@ -207,7 +207,9 @@ int do_page_fault(struct pt_regs *regs, unsigned long address, int trap = TRAP(regs); int is_exec = trap == 0x400; int fault; - int rc = 0, store_update_sp = 0; + int rc = 0; + int is_user = user_mode(regs); + unsigned int inst = 0; #if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE)) /* @@ -216,7 +218,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address, * bits we are interested in. But there are some bits which * indicate errors in DSISR but can validly be set in SRR1. */ - if (trap == 0x400) + if (is_exec) error_code &= 0x48200000; else is_write = error_code & DSISR_ISSTORE; @@ -247,13 +249,13 @@ int do_page_fault(struct pt_regs *regs, unsigned long address, * The kernel should never take an execute fault nor should it * take a page fault to a kernel address. */ - if (!user_mode(regs) && (is_exec || (address >= TASK_SIZE))) { + if (!is_user && (is_exec || (address >= TASK_SIZE))) { rc = SIGSEGV; goto bail; } #if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE) || \ - defined(CONFIG_PPC_BOOK3S_64)) + defined(CONFIG_PPC_BOOK3S_64) || defined(CONFIG_PPC_8xx)) if (error_code & DSISR_DABRMATCH) { /* breakpoint match */ do_break(regs, address, error_code); @@ -266,7 +268,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address, local_irq_enable(); if (faulthandler_disabled() || mm == NULL) { - if (!user_mode(regs)) { + if (!is_user) { rc = SIGSEGV; goto bail; } @@ -287,10 +289,10 @@ 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_exec && user_mode(regs)) - store_update_sp = store_updates_sp(regs); + if (is_write && is_user) + __get_user(inst, (unsigned int __user *)regs->nip); - if (user_mode(regs)) + if (is_user) flags |= FAULT_FLAG_USER; /* When running in the kernel we expect faults to occur only to @@ -309,7 +311,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address, * thus avoiding the deadlock. */ if (!down_read_trylock(&mm->mmap_sem)) { - if (!user_mode(regs) && !search_exception_tables(regs->nip)) + if (!is_user && !search_exception_tables(regs->nip)) goto bad_area_nosemaphore; retry: @@ -358,7 +360,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address, * between the last mapped region and the stack will * expand the stack rather than segfaulting. */ - if (address + 2048 < uregs->gpr[1] && !store_update_sp) + if (address + 2048 < uregs->gpr[1] && !store_updates_sp(inst)) goto bad_area; } if (expand_stack(vma, address)) @@ -509,7 +511,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address, bad_area_nosemaphore: /* User mode accesses cause a SIGSEGV */ - if (user_mode(regs)) { + if (is_user) { _exception(SIGSEGV, regs, code, address); goto bail; } -- 2.12.0