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Date: Sun, 3 Apr 2016 08:52:35 +0300 From: Konstantin Khlebnikov <koct9i@...il.com> To: Piotr Kwapulinski <kwapulinski.piotr@...il.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, Michal Hocko <mhocko@...e.com>, Michael Kerrisk-manpages <mtk.manpages@...il.com>, cmetcalf@...lanox.com, Arnd Bergmann <arnd@...db.de>, Al Viro <viro@...iv.linux.org.uk>, mszeredi@...e.cz, Davidlohr Bueso <dave@...olabs.net>, "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Vlastimil Babka <vbabka@...e.cz>, Ingo Molnar <mingo@...nel.org>, dan.j.williams@...el.com, Dave Hansen <dave.hansen@...ux.intel.com>, Johannes Weiner <hannes@...xchg.org>, Jan Kara <jack@...e.cz>, xiexiuqi@...wei.com, Joonsoo Kim <iamjoonsoo.kim@....com>, Oleg Nesterov <oleg@...hat.com>, Chen Gang <gang.chen.5i5j@...il.com>, Andrea Arcangeli <aarcange@...hat.com>, Andrey Ryabinin <aryabinin@...tuozzo.com>, David Rientjes <rientjes@...gle.com>, denc716@...il.com, toshi.kani@....com, ldufour@...ux.vnet.ibm.com, kuleshovmail@...il.com, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>, linux-arch <linux-arch@...r.kernel.org> Subject: Re: [PATCH 0/3] mm/mmap.c: don't unmap the overlapping VMA(s) On Sat, Apr 2, 2016 at 10:17 PM, Piotr Kwapulinski <kwapulinski.piotr@...il.com> wrote: > Currently the mmap(MAP_FIXED) discards the overlapping part of the > existing VMA(s). > Introduce the new MAP_DONTUNMAP flag which forces the mmap to fail > with ENOMEM whenever the overlapping occurs and MAP_FIXED is set. > No existing mapping(s) is discarded. How userspace is supposed to use this and handle failure? For now you can get the same behavior in couple syscalls: mmap without MAP_FIXED if resulting address differs unmmap and handle error. Twice slower but this is error-path so you anyway have to some extra actions. > The implementation tests the MAP_DONTUNMAP flag right before unmapping > the VMA. The tile arch is the dependency of mmap_flags. > > I did the isolated tests and also tested it with Gentoo full > installation. > > Signed-off-by: Piotr Kwapulinski <kwapulinski.piotr@...il.com> > --- > arch/tile/mm/elf.c | 1 + > include/linux/mm.h | 3 ++- > include/uapi/asm-generic/mman-common.h | 1 + > mm/mmap.c | 10 +++++++--- > 4 files changed, 11 insertions(+), 4 deletions(-) > > diff --git a/arch/tile/mm/elf.c b/arch/tile/mm/elf.c > index 6225cc9..dae4b33 100644 > --- a/arch/tile/mm/elf.c > +++ b/arch/tile/mm/elf.c > @@ -142,6 +142,7 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, > if (!retval) { > unsigned long addr = MEM_USER_INTRPT; > addr = mmap_region(NULL, addr, INTRPT_SIZE, > + MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE, > VM_READ|VM_EXEC| > VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC, 0); > if (addr > (unsigned long) -PAGE_SIZE) > diff --git a/include/linux/mm.h b/include/linux/mm.h > index ed6407d..31dcdfb 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -2048,7 +2048,8 @@ extern int install_special_mapping(struct mm_struct *mm, > extern unsigned long get_unmapped_area(struct file *, unsigned long, unsigned long, unsigned long, unsigned long); > > extern unsigned long mmap_region(struct file *file, unsigned long addr, > - unsigned long len, vm_flags_t vm_flags, unsigned long pgoff); > + unsigned long len, unsigned long mmap_flags, > + vm_flags_t vm_flags, unsigned long pgoff); > extern unsigned long do_mmap(struct file *file, unsigned long addr, > unsigned long len, unsigned long prot, unsigned long flags, > vm_flags_t vm_flags, unsigned long pgoff, unsigned long *populate); > diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h > index 5827438..3655be3 100644 > --- a/include/uapi/asm-generic/mman-common.h > +++ b/include/uapi/asm-generic/mman-common.h > @@ -19,6 +19,7 @@ > #define MAP_TYPE 0x0f /* Mask for type of mapping */ > #define MAP_FIXED 0x10 /* Interpret addr exactly */ > #define MAP_ANONYMOUS 0x20 /* don't use a file */ > +#define MAP_DONTUNMAP 0x40 /* don't unmap overlapping VMA */ > #ifdef CONFIG_MMAP_ALLOW_UNINITIALIZED > # define MAP_UNINITIALIZED 0x4000000 /* For anonymous mmap, memory could be uninitialized */ > #else > diff --git a/mm/mmap.c b/mm/mmap.c > index bd2e1a53..ab429c3 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -1286,7 +1286,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr, > vm_flags |= VM_NORESERVE; > } > > - addr = mmap_region(file, addr, len, vm_flags, pgoff); > + addr = mmap_region(file, addr, len, flags, vm_flags, pgoff); > if (!IS_ERR_VALUE(addr) && > ((vm_flags & VM_LOCKED) || > (flags & (MAP_POPULATE | MAP_NONBLOCK)) == MAP_POPULATE)) > @@ -1422,7 +1422,8 @@ static inline int accountable_mapping(struct file *file, vm_flags_t vm_flags) > } > > unsigned long mmap_region(struct file *file, unsigned long addr, > - unsigned long len, vm_flags_t vm_flags, unsigned long pgoff) > + unsigned long len, unsigned long mmap_flags, > + vm_flags_t vm_flags, unsigned long pgoff) > { > struct mm_struct *mm = current->mm; > struct vm_area_struct *vma, *prev; > @@ -1448,7 +1449,10 @@ unsigned long mmap_region(struct file *file, unsigned long addr, > /* Clear old maps */ > while (find_vma_links(mm, addr, addr + len, &prev, &rb_link, > &rb_parent)) { > - if (do_munmap(mm, addr, len)) > + const bool dont_unmap = > + (mmap_flags & (MAP_DONTUNMAP | MAP_FIXED)) > + == (MAP_DONTUNMAP | MAP_FIXED); > + if (dont_unmap || do_munmap(mm, addr, len)) > return -ENOMEM; > } > > -- > 2.7.4 >
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