Re: [RFC PATCH v2 00/19] PKS write protected page tables

IIRC shoot-downs are one of the reasons for using per-cpu PGDs which would
be a hard sell to some people.
https://forum.osdev.org/viewtopic.php?f=15&t=29661

-Boris

On Thu, Mar 14, 2024 at 2:26 PM Ira Weiny <[email protected]> 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/
>
>
>

-- 
Boris Lukashev
Systems Architect
Semper Victus <https://www.sempervictus.com>