Messages in this thread | | | Date | Fri, 14 Jun 2019 16:28:36 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCH, RFC 13/62] x86/mm: Add hooks to allocate and free encrypted pages |
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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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