lkml.org 
[lkml]   [2020]   [Feb]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 5/5] arm64/vdso: Restrict splitting VVAR VMA
On Thu, Feb 20, 2020 at 12:22:52PM +0000, Vincenzo Frascino wrote:
> Hi Andrei,
>
> On 04/02/2020 17:59, Andrei Vagin wrote:
> > Forbid splitting VVAR VMA resulting in a stricter ABI and reducing the
> > amount of corner-cases to consider while working further on VDSO time
> > namespace support.
> >
> > As the offset from timens to VVAR page is computed compile-time, the pages
> > in VVAR should stay together and not being partically mremap()'ed.
> >
>
> I agree on the concept, but why do we need to redefine mremap?
> special_mapping_mremap() (mm/mmap.c +3317) seems doing already the same thing if
> we leave mremap == NULL as is.
>

Hmmm. I have read the code of special_mapping_mremap() and I don't see where
it restricts splitting the vvar mapping.

Here is the code what I see in the source:

static int special_mapping_mremap(struct vm_area_struct *new_vma)
{
struct vm_special_mapping *sm = new_vma->vm_private_data;

if (WARN_ON_ONCE(current->mm != new_vma->vm_mm))
return -EFAULT;

if (sm->mremap)
return sm->mremap(sm, new_vma);

return 0;
}

And I have checked that without this patch, I can remap only one page of
the vvar mapping.

Thanks,
Andrei

\
 
 \ /
  Last update: 2020-02-24 00:31    [W:0.120 / U:0.872 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site