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SubjectRe: [PATCH, RFC 13/62] x86/mm: Add hooks to allocate and free encrypted pages
On Fri, Jun 14, 2019 at 01:04:58PM +0200, Peter Zijlstra wrote:
> On Fri, Jun 14, 2019 at 11:34:09AM +0200, Peter Zijlstra wrote:
> > On Wed, May 08, 2019 at 05:43:33PM +0300, Kirill A. Shutemov wrote:
> >
> > > + lookup_page_ext(page)->keyid = keyid;
>
> > > + lookup_page_ext(page)->keyid = 0;
>
> Also, perhaps paranoid; but do we want something like:
>
> static inline void page_set_keyid(struct page *page, int keyid)
> {
> /* ensure nothing creeps after changing the keyid */
> barrier();
> WRITE_ONCE(lookup_page_ext(page)->keyid, keyid);
> barrier();
> /* ensure nothing creeps before changing the keyid */
> }
>
> And this is very much assuming there is no concurrency through the
> allocator locks.

There's no concurrency for this page: it has been off the free list, but
have not yet passed on to user. Nobody else sees the page before
allocation is finished.

And barriers/WRITE_ONCE() looks excessive to me. It's just yet another bit
of page's metadata and I don't see why it's has to be handled in a special
way.

Does it relax your paranoia? :P

--
Kirill A. Shutemov

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