On Fri, Oct 06, 2023 at 02:24:11PM -0500, Kalra, Ashish wrote:
>
> On 10/5/2023 5:28 PM, Kirill A. Shutemov wrote:
> > On Thu, Oct 05, 2023 at 05:01:23PM -0500, Kalra, Ashish wrote:
> > > On 10/5/2023 4:28 PM, Kirill A. Shutemov wrote:
> > > > On Thu, Oct 05, 2023 at 01:41:38PM -0500, Kalra, Ashish wrote:
> > > > > > +static void unshare_all_memory(bool unmap)
> > > > > > +{
> > > > > > + unsigned long addr, end;
> > > > > > + long found = 0, shared;
> > > > > > +
> > > > > > + /*
> > > > > > + * Walk direct mapping and convert all shared memory back to
> > > > > > private,
> > > > > > + */
> > > > > > +
> > > > > > + addr = PAGE_OFFSET;
> > > > > > + end = PAGE_OFFSET + get_max_mapped();
> > > > > > +
> > > > > > + while (addr < end) {
> > > > > > + unsigned long size;
> > > > > > + unsigned int level;
> > > > > > + pte_t *pte;
> > > > > > +
> > > > > > + pte = lookup_address(addr, &level);
> > > > >
> > > > > IIRC, you were earlier walking the direct mapping using
> > > > > walk_page_range_novma(), any particular reason to use lookup_address()
> > > > > instead ?
> > > >
> > > > walk_page_range_novma() wants mmap lock to be taken, but it is tricky as
> > > > we run here from atomic context in case of crash.
> > > >
> > > > I considered using trylock to bypass the limitation, but it is a hack.
> > > >
> > > > >
> > > > > > + size = page_level_size(level);
> > > > > > +
> > > > > > + if (pte && pte_decrypted(*pte)) {
> > > > >
> > > > > Additionally need to add check for pte_none() here to handle physical
> > > > > memory
> > > > > holes in direct mapping.
> > > >
> > > > lookup_address() returns NULL for none entries.
> > > >
> > >
> > > Looking at lookup_address_in_pgd(), at pte level it is simply returning
> > > pte_offset_kernel() and there does not seem to be a check for returning
> > > NULL
> > > if pte_none() ?
> >
> > Hm. You are right.
> >
> > I think it yet another quirk in how lookup_address() implemented. We need
> > to make it straight too.
> >
> > There's two options: either make lookup_address() return pointer for entry
> > even if it is NULL, or add check for pte_none() after pte_offset_kernel()
> > and return NULL if it is true.
> >
> > I like the first option more as it allows caller to populate the entry if
> > it wants.
>
> Yes, i like the first option.
I tried to this, but lookup_address() has to many callers. It gets beyond
the scope of the patchset. I will add pte_none() check on unshare side for
now.
--
Kiryl Shutsemau / Kirill A. Shutemov
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