IIRC shoot-downs are one of the reasons for using per-cpu PGDs which would be a hard sell to some people.
-Boris
On Thu, Mar 14, 2024 at 2:26 PM Ira Weiny <ira.weiny@xxxxxxxxx> wrote:
Edgecombe, Rick P wrote:
> On Thu, 2024-03-14 at 09:27 -0700, Kees Cook wrote:
> > On Mon, Aug 30, 2021 at 04:59:08PM -0700, Rick Edgecombe wrote:
> > > This is a second RFC for the PKS write protected tables concept.
> > > I'm sharing to
> > > show the progress to interested people. I'd also appreciate any
> > > comments,
> > > especially on the direct map page table protection solution (patch
> > > 17).
> >
> > *thread necromancy*
> >
> > Hi,
> >
> > Where does this series stand? I don't think it ever got merged?
>
> There are sort of three components to this:
> 1. Basic PKS support. It was dropped after the main use case was
> rejected (pmem stray write protection).
This was the main reason it got dropped.
> 2. Solution for applying direct map permissions efficiently. This
> includes avoiding excessive kernel shootdowns, as well as avoiding
> direct map fragmentation. rppt continued to look at the fragmentation
> part of the problem and ended up arguing that it actually isn't an
> issue [0]. Regardless, the shootdown problem remains for usages like
> PKS tables that allocate so frequently. There is an attempt to address
> both in this series. But given the above, there may be lots of debate
> and opinions.
> 3. The actual protection of the PKS tables (most of this series). It
> got paused when I started to work on CET. In the meantime 1 was
> dropped, and 2 is still open(?). So there is more to work through now,
> then when it was dropped.
>
> If anyone wants to pick it up, it is fine by me. I can help with
> reviews.
I can help with reviews as well,
Ira
>
>
> [0] https://lwn.net/Articles/931406/
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