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SubjectRe: [PATCH 00/31 v2] PTI support for x86_32
On Fri, Feb 09, 2018 at 08:11:12PM +0100, Joerg Roedel wrote:
> On Fri, Feb 09, 2018 at 05:47:43PM +0000, Andy Lutomirski wrote:
> > One thing worth noting is that performance of this whole series is
> > going to be abysmal due to the complete lack of 32-bit PCID. Maybe
> > any kernel built with this option set that runs on a CPU that has the
> > PCID bit set in CPUID should print a big fat warning like "WARNING:
> > you are using 32-bit PTI on a 64-bit PCID-capable CPU. Your
> > performance will increase dramatically if you switch to a 64-bit
> > kernel."
> Thanks for your review. I can add this warning, but I just hope that not
> a lot of people will actually see it :)

Alas, we got some data: says 20% of x86 users have i386 as their main ABI
(current; people with popcon installed).

Of those, 80% use 32-bit kernels: i686 881, x86_64 229, i586 14
(uname -m included in bug reports; data for 2016) -- and bug reporters tend
to have more clue than the average user. There's no way so many folks still
use pre-2004 computers.

Thus, if you could include that big fat warning, distro developers would be
thankful. Make it show fiery letters if you can. Preferably, we'd want a
huge mallet reach out of the screen and bonk the user on the head, but with
that impossible, a scary message would help.

Let them use 32-bit userland, but if someone runs such a kernel on a modern
machine, some kind of verbal abuse is warranted.

⣾⠁⢰⠒⠀⣿⡁ Vat kind uf sufficiently advanced technology iz dis!?
⢿⡄⠘⠷⠚⠋⠀ -- Genghis Ht'rok'din

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