On Mon, Feb 15, 2016 at 12:26 PM, Kirill A. Shutemov <kirill.shute...@linux.intel.com> wrote: > On Mon, Feb 15, 2016 at 03:32:55AM +0200, Grazvydas Ignotas wrote: >> Hi, >> >> since remap_file_pages() rework the following simple program fails. >> I haven't actually bisected this, only know it worked on 3.19 at least >> (I bought a new system now and need 4.2+ for hardware support). > > The patch below should fix the issue. Please test.
It works, thanks. Tested-by: Grazvydas Ignotas <nota...@gmail.com> > >> If you are curious, the program is an emulator and is using >> remap_file_pages() to implement memory mirroring efficiently (and to >> remap things during run time). > > Could you elaborate on this? > > Why creating file on tmpfs/shmem (using memfd_create() for example) plus > plain mmap()s wouldn't work for you? It works, but remap_file_pages() is just more convenient, you don't need many mmap()/munmap() calls (less syscalls), and as the emulator needs to reconfigure the mappings during runtime (it's not a one time init thing), remap_file_pages() makes more sense. The reduced number of VMAs of the past was also a benefit I guess. Actually I'm not the author of the emulator in question, so I've asked the author to comment: --- quote --- One of the things we do with remap_file_pages is a mapping for the emulated system's VRAM. The system allows many different configurations of several differently sized VRAM banks to a 16MB area of address space. The banks are multiples of 16KB in size and their allocations are also 16KB aligned. With remap_file_pages we can map that entire space to an (in-memory) file and then arbitrarily map chunks of it as desired. We have an mmap-based fallback, but it requires us to manage a separate mmap for each 16KB region." --- end of quote --- Apparently the mentioned fallback was a compile time option, so I was hit with the issue after upgrading my machine. > <snip> > > Signed-off-by: Kirill A. Shutemov <kirill.shute...@linux.intel.com> Cc: stable? Fixes: c8d78c182 (I guess?) > Reported-by: Grazvydas Ignotas <nota...@gmail.com> > --- > mm/mmap.c | 34 +++++++++++++++++++++++++++++----- > 1 file changed, 29 insertions(+), 5 deletions(-) > > diff --git a/mm/mmap.c b/mm/mmap.c > index 2f2415a7a688..76d1ec29149b 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -2664,12 +2664,29 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, > start, unsigned long, size, > if (!vma || !(vma->vm_flags & VM_SHARED)) > goto out; > > - if (start < vma->vm_start || start + size > vma->vm_end) > + if (start < vma->vm_start) > goto out; > > - if (pgoff == linear_page_index(vma, start)) { > - ret = 0; > - goto out; > + if (start + size > vma->vm_end) { > + struct vm_area_struct *next; > + > + for (next = vma->vm_next; next; next = next->vm_next) { > + /* hole between vmas ? */ > + if (next->vm_start != next->vm_prev->vm_end) > + goto out; > + > + if (next->vm_file != vma->vm_file) > + goto out; > + > + if (next->vm_flags != vma->vm_flags) > + goto out; > + > + if (start + size <= next->vm_end) > + break; > + } > + > + if (!next) > + goto out; > } > > prot |= vma->vm_flags & VM_READ ? PROT_READ : 0; > @@ -2679,9 +2696,16 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, > start, unsigned long, size, > flags &= MAP_NONBLOCK; > flags |= MAP_SHARED | MAP_FIXED | MAP_POPULATE; > if (vma->vm_flags & VM_LOCKED) { > + struct vm_area_struct *tmp; > flags |= MAP_LOCKED; > + > /* drop PG_Mlocked flag for over-mapped range */ > - munlock_vma_pages_range(vma, start, start + size); > + for (tmp = vma; tmp->vm_start >= start + size; > + tmp = tmp->vm_next) { > + munlock_vma_pages_range(tmp, > + max(tmp->vm_start, start), > + min(tmp->vm_end, start + size)); > + } > } > > file = get_file(vma->vm_file); > -- > Kirill A. Shutemov GraÅžvydas