From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f175.google.com (mail-wi0-f175.google.com [209.85.212.175]) by kanga.kvack.org (Postfix) with ESMTP id 22E516B0253 for ; Mon, 13 Jul 2015 08:42:49 -0400 (EDT) Received: by wicmz13 with SMTP id mz13so60750599wic.0 for ; Mon, 13 Jul 2015 05:42:48 -0700 (PDT) Received: from mail-wi0-f169.google.com (mail-wi0-f169.google.com. [209.85.212.169]) by mx.google.com with ESMTPS id cw1si13257682wib.15.2015.07.13.05.42.47 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 13 Jul 2015 05:42:47 -0700 (PDT) Received: by wiga1 with SMTP id a1so68269031wig.0 for ; Mon, 13 Jul 2015 05:42:46 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20150713122920.32C8CA4@black.fi.intel.com> References: <1436784852-144369-1-git-send-email-kirill.shutemov@linux.intel.com> <1436784852-144369-3-git-send-email-kirill.shutemov@linux.intel.com> <20150713122920.32C8CA4@black.fi.intel.com> From: Leon Romanovsky Date: Mon, 13 Jul 2015 15:42:27 +0300 Message-ID: Subject: Re: [PATCH 2/5] x86, mpx: do not set ->vm_ops on mpx VMAs Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: "Kirill A. Shutemov" Cc: Andrew Morton , Oleg Nesterov , Linux-MM , "linux-kernel@vger.kernel.org" , Dave Hansen , Andy Lutomirski , Thomas Gleixner On Mon, Jul 13, 2015 at 3:29 PM, Kirill A. Shutemov wrote: > Leon Romanovsky wrote: >> Hi Kirill, >> >> On Mon, Jul 13, 2015 at 1:54 PM, Kirill A. Shutemov >> wrote: >> > >> > MPX setups private anonymous mapping, but uses vma->vm_ops too. >> > This can confuse core VM, as it relies on vm->vm_ops to distinguish >> > file VMAs from anonymous. >> > >> > As result we will get SIGBUS, because handle_pte_fault() thinks it's >> > file VMA without vm_ops->fault and it doesn't know how to handle the >> > situation properly. >> > >> > Let's fix that by not setting ->vm_ops. >> > >> > We don't really need ->vm_ops here: MPX VMA can be detected with VM_MPX >> > flag. And vma_merge() will not merge MPX VMA with non-MPX VMA, because >> > ->vm_flags won't match. >> > >> > The only thing left is name of VMA. I'm not sure if it's part of ABI, or >> > we can just drop it. The patch keep it by providing arch_vma_name() on x86. >> > >> > Build tested only. >> > >> > Signed-off-by: Kirill A. Shutemov >> > Cc: Dave Hansen >> > Cc: Andy Lutomirski >> > Cc: Thomas Gleixner >> > --- >> > arch/x86/mm/mmap.c | 7 +++++++ >> > arch/x86/mm/mpx.c | 20 +------------------- >> > 2 files changed, 8 insertions(+), 19 deletions(-) >> > >> > diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c >> > index 9d518d693b4b..844b06d67df4 100644 >> > --- a/arch/x86/mm/mmap.c >> > +++ b/arch/x86/mm/mmap.c >> > @@ -126,3 +126,10 @@ void arch_pick_mmap_layout(struct mm_struct *mm) >> > mm->get_unmapped_area = arch_get_unmapped_area_topdown; >> > } >> > } >> > + >> > +const char *arch_vma_name(struct vm_area_struct *vma) >> > +{ >> > + if (vma->vm_flags & VM_MPX) >> > + return "[mpx]"; >> > + return NULL; >> > +} >> >> I sure that I'm missing something important. This function stores >> "[mpx]" string on this function stack and returns the pointer to that >> address. In current flow, this address is visible and accessible, >> however in can be a different in general case. > > The string is not on stack. String literals are in .rodata and caller is > not allowed to modify it since it's "const char *". I see, it behaves similiar to global "const char *" variable definition. Thank you for clarification. > > -- > Kirill -- Leon Romanovsky | Independent Linux Consultant www.leon.nu | leon@leon.nu -- 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/ . Don't email: email@kvack.org