Re: [PATCH v2 1/6] mm: introduce vma->vm_flags modifier functions

On Wed, Jan 25, 2023 at 08:49:50AM -0800, Suren Baghdasaryan wrote:

On Wed, Jan 25, 2023 at 1:10 AM Peter Zijlstra peterz@infradead.org wrote:

...

...

• /*
  

•  * Flags, see mm.h.
  

•  * WARNING! Do not modify directly.
  

•  * Use {init|reset|set|clear|mod}_vm_flags() functions instead.
  

•  */
  

• unsigned long vm_flags;
  

We have __private and ACCESS_PRIVATE() to help with enforcing this.

Thanks for pointing this out, Peter! I guess for that I'll need to convert all read accesses and provide get_vm_flags() too? That will cause some additional churt (a quick search shows 801 hits over 248 files) but maybe it's worth it? I think Michal suggested that too in another patch. Should I do that while we are at it?

Here's a trick I saw somewhere in the VFS:

union { const vm_flags_t vm_flags; vm_flags_t __private __vm_flags; };

Now it can be read by anybody but written only by those using ACCESS_PRIVATE.