From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751912Ab1GSEaM (ORCPT ); Tue, 19 Jul 2011 00:30:12 -0400 Received: from gate.crashing.org ([63.228.1.57]:33676 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750974Ab1GSEaL (ORCPT ); Tue, 19 Jul 2011 00:30:11 -0400 Subject: [RFC/PATCH] mm/futex: Fix futex writes on archs with SW tracking of dirty & young From: Benjamin Herrenschmidt To: Shan Hai Cc: Peter Zijlstra , Peter Zijlstra , paulus@samba.org, tglx@linutronix.de, walken@google.com, dhowells@redhat.com, cmetcalf@tilera.com, tony.luck@intel.com, akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org In-Reply-To: <4E24FA51.70602@gmail.com> References: <1310717238-13857-1-git-send-email-haishan.bai@gmail.com> <1310717238-13857-2-git-send-email-haishan.bai@gmail.com> <1310725418.2586.309.camel@twins> <4E21A526.8010904@gmail.com> <1310860194.25044.17.camel@pasglop> <4b337921-d430-4b63-bc36-ad31753cf800@email.android.com> <1310912990.25044.203.camel@pasglop> <1310944453.25044.262.camel@pasglop> <1310961691.25044.274.camel@pasglop> <4E23D728.7090406@gmail.com> <1310972462.25044.292.camel@pasglop> <4E23E02C.8090401@gmail.com> <1310974591.25044.298.camel@pasglop> <4E24FA51.70602@gmail.com> Content-Type: text/plain; charset="UTF-8" Date: Tue, 19 Jul 2011 14:29:22 +1000 Message-ID: <1311049762.25044.392.camel@pasglop> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The futex code currently attempts to write to user memory within a pagefault disabled section, and if that fails, tries to fix it up using get_user_pages(). This doesn't work on archs where the dirty and young bits are maintained by software, since they will gate access permission in the TLB, and will not be updated by gup(). In addition, there's an expectation on some archs that a spurious write fault triggers a local TLB flush, and that is missing from the picture as well. I decided that adding those "features" to gup() would be too much for this already too complex function, and instead added a new simpler fixup_user_fault() which is essentially a wrapper around handle_mm_fault() which the futex code can call. Signed-off-by: Benjamin Herrenschmidt --- Shan, can you test this ? It might not fix the problem since I'm starting to have the nasty feeling that you are hitting what is somewhat a subtly different issue or my previous patch should have worked (but then I might have done a stupid mistake as well) but let us know anyway. Cheers, Ben. diff --git a/include/linux/mm.h b/include/linux/mm.h index 9670f71..1036614 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -985,6 +985,8 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm, int get_user_pages_fast(unsigned long start, int nr_pages, int write, struct page **pages); struct page *get_dump_page(unsigned long addr); +extern int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm, + unsigned long address, unsigned int fault_flags); extern int try_to_release_page(struct page * page, gfp_t gfp_mask); extern void do_invalidatepage(struct page *page, unsigned long offset); diff --git a/kernel/futex.c b/kernel/futex.c index fe28dc2..7a0a4ed 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -355,8 +355,8 @@ static int fault_in_user_writeable(u32 __user *uaddr) int ret; down_read(&mm->mmap_sem); - ret = get_user_pages(current, mm, (unsigned long)uaddr, - 1, 1, 0, NULL, NULL); + ret = fixup_user_fault(current, mm, (unsigned long)uaddr, + FAULT_FLAG_WRITE); up_read(&mm->mmap_sem); return ret < 0 ? ret : 0; diff --git a/mm/memory.c b/mm/memory.c index 40b7531..b967fb0 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1815,7 +1815,64 @@ next_page: } EXPORT_SYMBOL(__get_user_pages); -/** +/* + * fixup_user_fault() - manually resolve a user page fault + * @tsk: the task_struct to use for page fault accounting, or + * NULL if faults are not to be recorded. + * @mm: mm_struct of target mm + * @address: user address + * @fault_flags:flags to pass down to handle_mm_fault() + * + * This is meant to be called in the specific scenario where for + * locking reasons we try to access user memory in atomic context + * (within a pagefault_disable() section), this returns -EFAULT, + * and we want to resolve the user fault before trying again. + * + * Typically this is meant to be used by the futex code. + * + * The main difference with get_user_pages() is that this function + * will unconditionally call handle_mm_fault() which will in turn + * perform all the necessary SW fixup of the dirty and young bits + * in the PTE, while handle_mm_fault() only guarantees to update + * these in the struct page. + * + * This is important for some architectures where those bits also + * gate the access permission to the page because their are + * maintained in software. On such architecture, gup() will not + * be enough to make a subsequent access succeed. + * + * This should be called with the mm_sem held for read. + */ +int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm, + unsigned long address, unsigned int fault_flags) +{ + struct vm_area_struct *vma; + int ret; + + vma = find_extend_vma(mm, address); + if (!vma || address < vma->vm_start) + return -EFAULT; + + ret = handle_mm_fault(mm, vma, address, fault_flags); + if (ret & VM_FAULT_ERROR) { + if (ret & VM_FAULT_OOM) + return -ENOMEM; + if (ret & (VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE)) + return -EHWPOISON; + if (ret & VM_FAULT_SIGBUS) + return -EFAULT; + BUG(); + } + if (tsk) { + if (ret & VM_FAULT_MAJOR) + tsk->maj_flt++; + else + tsk->min_flt++; + } + return 0; +} + +/* * get_user_pages() - pin user pages in memory * @tsk: the task_struct to use for page fault accounting, or * NULL if faults are not to be recorded. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 7A7BDB6F69 for ; Tue, 19 Jul 2011 14:29:58 +1000 (EST) Subject: [RFC/PATCH] mm/futex: Fix futex writes on archs with SW tracking of dirty & young From: Benjamin Herrenschmidt To: Shan Hai In-Reply-To: <4E24FA51.70602@gmail.com> References: <1310717238-13857-1-git-send-email-haishan.bai@gmail.com> <1310717238-13857-2-git-send-email-haishan.bai@gmail.com> <1310725418.2586.309.camel@twins> <4E21A526.8010904@gmail.com> <1310860194.25044.17.camel@pasglop> <4b337921-d430-4b63-bc36-ad31753cf800@email.android.com> <1310912990.25044.203.camel@pasglop> <1310944453.25044.262.camel@pasglop> <1310961691.25044.274.camel@pasglop> <4E23D728.7090406@gmail.com> <1310972462.25044.292.camel@pasglop> <4E23E02C.8090401@gmail.com> <1310974591.25044.298.camel@pasglop> <4E24FA51.70602@gmail.com> Content-Type: text/plain; charset="UTF-8" Date: Tue, 19 Jul 2011 14:29:22 +1000 Message-ID: <1311049762.25044.392.camel@pasglop> Mime-Version: 1.0 Cc: tony.luck@intel.com, Peter Zijlstra , Peter Zijlstra , linux-kernel@vger.kernel.org, cmetcalf@tilera.com, dhowells@redhat.com, paulus@samba.org, tglx@linutronix.de, walken@google.com, linuxppc-dev@lists.ozlabs.org, akpm@linux-foundation.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , The futex code currently attempts to write to user memory within a pagefault disabled section, and if that fails, tries to fix it up using get_user_pages(). This doesn't work on archs where the dirty and young bits are maintained by software, since they will gate access permission in the TLB, and will not be updated by gup(). In addition, there's an expectation on some archs that a spurious write fault triggers a local TLB flush, and that is missing from the picture as well. I decided that adding those "features" to gup() would be too much for this already too complex function, and instead added a new simpler fixup_user_fault() which is essentially a wrapper around handle_mm_fault() which the futex code can call. Signed-off-by: Benjamin Herrenschmidt --- Shan, can you test this ? It might not fix the problem since I'm starting to have the nasty feeling that you are hitting what is somewhat a subtly different issue or my previous patch should have worked (but then I might have done a stupid mistake as well) but let us know anyway. Cheers, Ben. diff --git a/include/linux/mm.h b/include/linux/mm.h index 9670f71..1036614 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -985,6 +985,8 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm, int get_user_pages_fast(unsigned long start, int nr_pages, int write, struct page **pages); struct page *get_dump_page(unsigned long addr); +extern int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm, + unsigned long address, unsigned int fault_flags); extern int try_to_release_page(struct page * page, gfp_t gfp_mask); extern void do_invalidatepage(struct page *page, unsigned long offset); diff --git a/kernel/futex.c b/kernel/futex.c index fe28dc2..7a0a4ed 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -355,8 +355,8 @@ static int fault_in_user_writeable(u32 __user *uaddr) int ret; down_read(&mm->mmap_sem); - ret = get_user_pages(current, mm, (unsigned long)uaddr, - 1, 1, 0, NULL, NULL); + ret = fixup_user_fault(current, mm, (unsigned long)uaddr, + FAULT_FLAG_WRITE); up_read(&mm->mmap_sem); return ret < 0 ? ret : 0; diff --git a/mm/memory.c b/mm/memory.c index 40b7531..b967fb0 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1815,7 +1815,64 @@ next_page: } EXPORT_SYMBOL(__get_user_pages); -/** +/* + * fixup_user_fault() - manually resolve a user page fault + * @tsk: the task_struct to use for page fault accounting, or + * NULL if faults are not to be recorded. + * @mm: mm_struct of target mm + * @address: user address + * @fault_flags:flags to pass down to handle_mm_fault() + * + * This is meant to be called in the specific scenario where for + * locking reasons we try to access user memory in atomic context + * (within a pagefault_disable() section), this returns -EFAULT, + * and we want to resolve the user fault before trying again. + * + * Typically this is meant to be used by the futex code. + * + * The main difference with get_user_pages() is that this function + * will unconditionally call handle_mm_fault() which will in turn + * perform all the necessary SW fixup of the dirty and young bits + * in the PTE, while handle_mm_fault() only guarantees to update + * these in the struct page. + * + * This is important for some architectures where those bits also + * gate the access permission to the page because their are + * maintained in software. On such architecture, gup() will not + * be enough to make a subsequent access succeed. + * + * This should be called with the mm_sem held for read. + */ +int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm, + unsigned long address, unsigned int fault_flags) +{ + struct vm_area_struct *vma; + int ret; + + vma = find_extend_vma(mm, address); + if (!vma || address < vma->vm_start) + return -EFAULT; + + ret = handle_mm_fault(mm, vma, address, fault_flags); + if (ret & VM_FAULT_ERROR) { + if (ret & VM_FAULT_OOM) + return -ENOMEM; + if (ret & (VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE)) + return -EHWPOISON; + if (ret & VM_FAULT_SIGBUS) + return -EFAULT; + BUG(); + } + if (tsk) { + if (ret & VM_FAULT_MAJOR) + tsk->maj_flt++; + else + tsk->min_flt++; + } + return 0; +} + +/* * get_user_pages() - pin user pages in memory * @tsk: the task_struct to use for page fault accounting, or * NULL if faults are not to be recorded.