Re: [PATCH v8 9/9] vmcore: support mmap() on /proc/vmcore

[Maxim Uvarov <muvarov@gmail.com>]

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2013/5/24 Andrew Morton <akpm@linux-foundation.org>

> On Thu, 23 May 2013 14:25:48 +0900 HATAYAMA Daisuke <
> d.hatayama@jp.fujitsu.com> wrote:
>
> > This patch introduces mmap_vmcore().
> >
> > Don't permit writable nor executable mapping even with mprotect()
> > because this mmap() is aimed at reading crash dump memory.
> > Non-writable mapping is also requirement of remap_pfn_range() when
> > mapping linear pages on non-consecutive physical pages; see
> > is_cow_mapping().
> >
> > Set VM_MIXEDMAP flag to remap memory by remap_pfn_range and by
> > remap_vmalloc_range_pertial at the same time for a single
> > vma. do_munmap() can correctly clean partially remapped vma with two
> > functions in abnormal case. See zap_pte_range(), vm_normal_page() and
> > their comments for details.
> >
> > On x86-32 PAE kernels, mmap() supports at most 16TB memory only. This
> > limitation comes from the fact that the third argument of
> > remap_pfn_range(), pfn, is of 32-bit length on x86-32: unsigned long.
>
> More reviewing and testing, please.
>
>
Do you have git pull for both kernel and userland changes? I would like to
do some more testing on my machines.

Maxim.


>
> From: Andrew Morton <akpm@linux-foundation.org>
> Subject: vmcore-support-mmap-on-proc-vmcore-fix
>
> use min(), switch to conventional error-unwinding approach
>
> Cc: Atsushi Kumagai <kumagai-atsushi@mxc.nes.nec.co.jp>
> Cc: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> Cc: Lisa Mitchell <lisa.mitchell@hp.com>
> Cc: Vivek Goyal <vgoyal@redhat.com>
> Cc: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
>
>  fs/proc/vmcore.c |   27 ++++++++++-----------------
>  1 file changed, 10 insertions(+), 17 deletions(-)
>
> diff -puN fs/proc/vmcore.c~vmcore-support-mmap-on-proc-vmcore-fix
> fs/proc/vmcore.c
> --- a/fs/proc/vmcore.c~vmcore-support-mmap-on-proc-vmcore-fix
> +++ a/fs/proc/vmcore.c
> @@ -218,9 +218,7 @@ static int mmap_vmcore(struct file *file
>         if (start < elfcorebuf_sz) {
>                 u64 pfn;
>
> -               tsz = elfcorebuf_sz - start;
> -               if (size < tsz)
> -                       tsz = size;
> +               tsz = min(elfcorebuf_sz - (size_t)start, size);
>                 pfn = __pa(elfcorebuf + start) >> PAGE_SHIFT;
>                 if (remap_pfn_range(vma, vma->vm_start, pfn, tsz,
>                                     vma->vm_page_prot))
> @@ -236,15 +234,11 @@ static int mmap_vmcore(struct file *file
>         if (start < elfcorebuf_sz + elfnotes_sz) {
>                 void *kaddr;
>
> -               tsz = elfcorebuf_sz + elfnotes_sz - start;
> -               if (size < tsz)
> -                       tsz = size;
> +               tsz = min(elfcorebuf_sz + elfnotes_sz - (size_t)start,
> size);
>                 kaddr = elfnotes_buf + start - elfcorebuf_sz;
>                 if (remap_vmalloc_range_partial(vma, vma->vm_start + len,
> -                                               kaddr, tsz)) {
> -                       do_munmap(vma->vm_mm, vma->vm_start, len);
> -                       return -EAGAIN;
> -               }
> +                                               kaddr, tsz))
> +                       goto fail;
>                 size -= tsz;
>                 start += tsz;
>                 len += tsz;
> @@ -257,16 +251,12 @@ static int mmap_vmcore(struct file *file
>                 if (start < m->offset + m->size) {
>                         u64 paddr = 0;
>
> -                       tsz = m->offset + m->size - start;
> -                       if (size < tsz)
> -                               tsz = size;
> +                       tsz = min_t(size_t, m->offset + m->size - start,
> size);
>                         paddr = m->paddr + start - m->offset;
>                         if (remap_pfn_range(vma, vma->vm_start + len,
>                                             paddr >> PAGE_SHIFT, tsz,
> -                                           vma->vm_page_prot)) {
> -                               do_munmap(vma->vm_mm, vma->vm_start, len);
> -                               return -EAGAIN;
> -                       }
> +                                           vma->vm_page_prot))
> +                               goto fail;
>                         size -= tsz;
>                         start += tsz;
>                         len += tsz;
> @@ -277,6 +267,9 @@ static int mmap_vmcore(struct file *file
>         }
>
>         return 0;
> +fail:
> +       do_munmap(vma->vm_mm, vma->vm_start, len);
> +       return -EAGAIN;
>  }
>
>  static const struct file_operations proc_vmcore_operations = {
> _
>
>
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-- 
Best regards,
Maxim Uvarov

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