Re: [Part1 PATCH v4 15/17] percpu: introduce DEFINE_PER_CPU_UNENCRYPTED

[Brijesh Singh]

On 09/20/2017 02:34 AM, Borislav Petkov wrote:
> On Tue, Sep 19, 2017 at 08:50:20AM -0500, Brijesh Singh wrote:
> > "..shared_aligned" section does not start and end with page-size alignment.
>
> Nowhere in the code there's a comment saying: "This percpu section really must
> be page-size aligned because <reasons>." You need to be more verbose
> with requirements like that.

I will add that comment.


> Also, you're ending up needing a whole page per-CPU for those variables.
> And now with the alignment before and after, you have worst-case two
> pages fragmentation of percpu memory and percpu memory is a rather
> limited resource AFAIR.
>
> If only there were a alloc_percpu_page()...
>
> > Since the C-bit works on PAGE_SIZE alignment hence the "..unencrypted" section
>
> Btw, call that section "..decrypted" and everywhere do
> s/unencrypted/decrypted/g.

Will do


> > starts and ends with page-size alignment. The closest I can find is
> > "..page_aligned" but again it does not end with page-size alignment.
> >
> > Additionally, since we clear the C-bit from unencrypted section hence we
> > should avoid overloading the existing section -- we don't want to expose more
> > than we wish.
>
> Add that to the comment too.

Will do