From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx155.postini.com [74.125.245.155]) by kanga.kvack.org (Postfix) with SMTP id 9D5356B00E9 for ; Tue, 3 Apr 2012 10:38:06 -0400 (EDT) Date: Tue, 3 Apr 2012 16:37:52 +0200 From: Oleg Nesterov Subject: Re: [PATCH RFC] mm: account VMA before forced-COW via /proc/pid/mem Message-ID: <20120403143752.GA5150@redhat.com> References: <20120402153631.5101.44091.stgit@zurg> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120402153631.5101.44091.stgit@zurg> Sender: owner-linux-mm@kvack.org List-ID: To: Konstantin Khlebnikov Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hugh Dickins , Andrew Morton , Linus Torvalds On 04/02, Konstantin Khlebnikov wrote: > > Currently kernel does not account read-only private mappings into memory commitment. > But these mappings can be force-COW-ed in get_user_pages(). Heh. tail -n3 Documentation/vm/overcommit-accounting may be you should update it then. Can't really comment the patch, this is not my area. Still, > + down_write(&mm->mmap_sem); > + *pvma = vma = find_vma(mm, addr); > + if (vma && vma->vm_start <= addr) { > + ret = vma->vm_end - addr; > + if ((vma->vm_flags & (VM_ACCOUNT | VM_NORESERVE | VM_SHARED | > + VM_HUGETLB | VM_MAYWRITE)) == VM_MAYWRITE) { > + if (!security_vm_enough_memory_mm(mm, vma_pages(vma))) Oooooh, the whole vma. Say, gdb installs the single breakpoint into the huge .text mapping... I am not sure, but probably you want to check at least VM_IO/PFNMAP as well. We do not want to charge this memory and retry with FOLL_FORCE before vm_ops->access(). Say, /dev/mem. Hmm. OTOH, if I am right then mprotect_fixup() should be fixed?? We drop ->mmap_sem... Say, the task does mremap() in between and len == 2 * PAGE_SIZE. Then, for example, copy_to_user_page() can write to the same page twice. Perhaps not a problem in practice, I dunno. Oleg. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org