From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: [PATCH v3 2/2] powerpc/mm: Tracking vDSO remap Date: Thu, 26 Mar 2015 10:48:44 +0100 Message-ID: <20150326094844.GB15407@gmail.com> References: <20150325121118.GA2542@gmail.com> <20150325183316.GA9090@gmail.com> <1427317797.6468.86.camel@kernel.crashing.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1427317797.6468.86.camel@kernel.crashing.org> Sender: linux-kernel-owner@vger.kernel.org To: Benjamin Herrenschmidt Cc: Laurent Dufour , Paul Mackerras , Michael Ellerman , Jeff Dike , Richard Weinberger , Guan Xuetao , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, Arnd Bergmann , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, user-mode-linux-devel@lists.sourceforge.net, user-mode-linux-user@lists.sourceforge.net, linux-arch@vger.kernel.org, linux-mm@kvack.org, cov@codeaurora.org, criu@openvz.org List-Id: linux-arch.vger.kernel.org * Benjamin Herrenschmidt 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. > > > > In particular, what happens if an mremap() is done with > > old_start == vdso_base, but a shorter end than the end of the vDSO? > > (i.e. a partial mremap() with fewer pages than the vDSO size) > > Is there a way to forbid splitting ? Does x86 deal with that case at > all or it doesn't have to for some other reason ? So we use _install_special_mapping() - maybe PowerPC does that too? That adds VM_DONTEXPAND which ought to prevent some - but not all - of the VM API weirdnesses. On x86 we'll just dump core if someone unmaps the vdso. Thanks, Ingo From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f179.google.com ([209.85.212.179]:38342 "EHLO mail-wi0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750881AbbCZJsu (ORCPT ); Thu, 26 Mar 2015 05:48:50 -0400 Date: Thu, 26 Mar 2015 10:48:44 +0100 From: Ingo Molnar Subject: Re: [PATCH v3 2/2] powerpc/mm: Tracking vDSO remap Message-ID: <20150326094844.GB15407@gmail.com> References: <20150325121118.GA2542@gmail.com> <20150325183316.GA9090@gmail.com> <1427317797.6468.86.camel@kernel.crashing.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1427317797.6468.86.camel@kernel.crashing.org> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Benjamin Herrenschmidt Cc: Laurent Dufour , Paul Mackerras , Michael Ellerman , Jeff Dike , Richard Weinberger , Guan Xuetao , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, Arnd Bergmann , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, user-mode-linux-devel@lists.sourceforge.net, user-mode-linux-user@lists.sourceforge.net, linux-arch@vger.kernel.org, linux-mm@kvack.org, cov@codeaurora.org, criu@openvz.org Message-ID: <20150326094844.tJ2K6VRyCC97N-ttdhu273qadGby0MxbV417FS5rJYw@z> * Benjamin Herrenschmidt 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. > > > > In particular, what happens if an mremap() is done with > > old_start == vdso_base, but a shorter end than the end of the vDSO? > > (i.e. a partial mremap() with fewer pages than the vDSO size) > > Is there a way to forbid splitting ? Does x86 deal with that case at > all or it doesn't have to for some other reason ? So we use _install_special_mapping() - maybe PowerPC does that too? That adds VM_DONTEXPAND which ought to prevent some - but not all - of the VM API weirdnesses. On x86 we'll just dump core if someone unmaps the vdso. Thanks, Ingo