Re: [bug report] mm: replace vma->vm_flags direct modifications with modifier calls

[Yan Zhao <yan.y.zhao@intel.com>]

On Mon, Jul 17, 2023 at 09:18:34AM -0700, Suren Baghdasaryan wrote:
> On Sun, Jul 16, 2023 at 11:40 PM Yan Zhao <yan.y.zhao@intel.com> wrote:
> >
> > On Wed, Jul 12, 2023 at 07:48:06PM +0000, Suren Baghdasaryan wrote:
> > > > Would we be able to fix it in stable simply by not triggering the
> > > > vm_flags_set() in case these flags are already set?
> > >
> > > I think we can do that. gru_file_mmap() sets all the flags that are
> > > set by remap_pfn_range_notrack() (VM_IO | VM_PFNMAP | VM_DONTEXPAND |
> > > VM_DONTDUMP), so we can check if all bits are already present and skip
> > > the vm_flags_set() call.
> > >
> > But on x86, remap_pfn_range() also sets flag VM_PAT. (in track_pfn_remap()).
> >
> > Is there any interface to allow device driver to pre-set this flag in .mmap()
> > before .fault()? e.g. export track_pfn_remap() ?
> 
> Driver should be able to call vm_flags_set() in its .mmap().

Do you mean do something like this in .mmap()?

	flags = VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;
	#ifdef CONFIG_X86
	flags |= VM_PAT;
	#endif
	vm_flags_set(vma, flags);

But VM_PAT cannot be set until after a successful reserve_pfn_range(),
which function is again not exported.