From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-x22c.google.com (mail-wi0-x22c.google.com [IPv6:2a00:1450:400c:c05::22c]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 88A9D1A0688 for ; Thu, 26 Mar 2015 20:43:38 +1100 (AEDT) Received: by wibg7 with SMTP id g7so141398965wib.1 for ; Thu, 26 Mar 2015 02:43:35 -0700 (PDT) Sender: Ingo Molnar Date: Thu, 26 Mar 2015 10:43:30 +0100 From: Ingo Molnar To: Benjamin Herrenschmidt Subject: Re: [PATCH v3 2/2] powerpc/mm: Tracking vDSO remap Message-ID: <20150326094330.GA15407@gmail.com> References: <20150325121118.GA2542@gmail.com> <20150325183316.GA9090@gmail.com> <20150325183647.GA9331@gmail.com> <1427317867.6468.87.camel@kernel.crashing.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1427317867.6468.87.camel@kernel.crashing.org> Cc: linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, Laurent Dufour , user-mode-linux-devel@lists.sourceforge.net, Arnd Bergmann , Jeff Dike , "H. Peter Anvin" , x86@kernel.org, linux-kernel@vger.kernel.org, criu@openvz.org, linux-mm@kvack.org, Ingo Molnar , Paul Mackerras , cov@codeaurora.org, user-mode-linux-user@lists.sourceforge.net, Richard Weinberger , Thomas Gleixner , Guan Xuetao , linuxppc-dev@lists.ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , * Benjamin Herrenschmidt wrote: > On Wed, 2015-03-25 at 19:36 +0100, Ingo Molnar wrote: > > * Ingo Molnar wrote: > > > > > > +#define __HAVE_ARCH_REMAP > > > > +static inline void arch_remap(struct mm_struct *mm, > > > > + unsigned long old_start, unsigned long old_end, > > > > + unsigned long new_start, unsigned long new_end) > > > > +{ > > > > + /* > > > > + * mremap() doesn't allow moving multiple vmas so we can limit the > > > > + * check to old_start == vdso_base. > > > > + */ > > > > + if (old_start == mm->context.vdso_base) > > > > + mm->context.vdso_base = new_start; > > > > +} > > > > > > mremap() doesn't allow moving multiple vmas, but it allows the > > > movement of multi-page vmas and it also allows partial mremap()s, > > > where it will split up a vma. > > > > I.e. mremap() supports the shrinking (and growing) of vmas. In that > > case mremap() will unmap the end of the vma and will shrink the > > remaining vDSO vma. > > > > Doesn't that result in a non-working vDSO that should zero out > > vdso_base? > > Right. Now we can't completely prevent the user from shooting itself > in the foot I suppose, though there is a legit usage scenario which > is to move the vDSO around which it would be nice to support. I > think it's reasonable to put the onus on the user here to do the > right thing. I argue we should use the right condition to clear vdso_base: if the vDSO gets at least partially unmapped. Otherwise there's little point in the whole patch: either correctly track whether the vDSO is OK, or don't ... There's also the question of mprotect(): can users mprotect() the vDSO on PowerPC? Thanks, Ingo