Re: [RFC PATCH 1/3] mm/memory.c: convert __copy_remote_vm_str() to folios

[Matthew Wilcox]

On Wed, Jun 25, 2025 at 07:00:22PM +0100, Matthew Wilcox wrote:
> > +		folio_offset = offset_in_folio(folio, addr);
> 
> Umm.  Not sure this is safe.  A folio might be mapped misaligned, so
> 'addr' might not give you the right offset within the folio.  I think
> you might need to use addr - (vma->vm_pgoff << PAGE_SHIFT).  But I'd
> defer to others here ... particularly when it comes to anonymous folios.

Sorry, this calculation is obviously wrong.  It should be something like
the calculation in linear_page_index(), only without throwing away the
bottom PAGE_SHIFT bits.  But that's for file VMAs only, and I'm not sure
what should be done for anon vmas.  Possibly there is no way?