Re: [PATCH v1 1/3] xen/riscv: introduce setup_initial_pages

[Oleksii <oleksii.kurochko@gmail.com>]

> 
> > 
> > > > 
> > > > > +
> > > > > +    page_addr = map_start;
> > > > > +    while ( page_addr < map_end )
> > > > 
> > > > Looking at the loop, it looks like you are assuming that the
> > > > region
> > > > will
> > > > never cross a boundary of a page-table (either L0, L1, L2). I
> > > > am
> > > > not
> > > > convinced you can make such assumption (see below).
> > > > 
> > > > But if you really want to make such assumption then you should
> > > > add
> > > > some
> > > > guard (either BUILD_BUG_ON(), ASSERT(), proper check) in your
> > > > code to
> > > > avoid any surprise in the future.
> > > I am not sure that I fully understand what is the problem here.
> > > The address is aligned on (1<<12) boundary and each itearation is
> > > mapped (1<<12) page so all looks fine or I misunderstood you.
> > 
> > Let's take an example, imagine the region you want to map is 4MB. 
> > AFAICT, you are only passing one L0 page-table. So your code will
> > end
> > up 
> > to overwrite the previous entries in the zeroeth page-table and
> > then
> > add 
> > another link in the L1 page-table.
> Got it. Then it looks that current approach isn't correct totally...
Or as an option we can add to xen.lds.S something like:

  ASSERT(_end - _start <= MB(L0_ENTRIES*PAGE_SIZE), "Xen too large")

~ Oleksii