Spectre V2 & Meltdown Linux Fixes Might Get Disabled For Atom N270 & Other In-Order CPUs

[phoronix]

Phoronix: Spectre V2 & Meltdown Linux Fixes Might Get Disabled For Atom N270 & Other In-Order CPUs

There's a suggestion/proposal to disable the Spectre Variant Two and Meltdown mitigation by default with the Linux kernel for in-order CPUs...

http://www.phoronix.com/scan.php?page=news_item&px=Disable-V2-KPTI-For-In-Order-HW

[oleyska]

Let's just assume anything is bad.
Well, it's an Ok stance but someone had to know on top of their head ? someone!?

I remember those cpu's were brought up really early in the discussion regarding meltdown, like always in the top page of discussions.
Kind of surprised they didn't already do it.

[dungeon]

Isn't Atom N270 32bit only CPU, thus Meltdown mitigation isn't available for these?

If that is true, no idea how could someone asks that something which isn't enabled to be disabled

[tildearrow]

spectre_v2=off? I thought it only was "nopti noretpoline"...
What are all options to disable mitigation entirely?

[schmidtbag]

Isn't Atom N270 32bit only CPU, thus Meltdown mitigation isn't available for these?

If that is true, no idea how could someone asks that something which isn't enabled to be disabled

To my understanding, meltdown isn't specific to x86 or any sub-variants. I'm pretty sure even PPC and ARM are vulnerable.

[dungeon]

To my understanding, meltdown isn't specific to x86 or any sub-variants. I'm pretty sure even PPC and ARM are vulnerable.

Yes Meltdown is not specific to Intel, i don't talk about that. While it is enabled for 64bit, PTI is not enabled also for 32bit x86 OS... there is guy from Suse who is working on it, reaching v6 recently:

https://git.kernel.org/pub/scm/linux...oro/linux.git/

But i don't see that code in regular upstream kernels... well, maybe Suse distro kernels enabling that, no idea there

So, still no idea how could someone asks on kernel mailing list that something which isn't enabled to be disabled

[euler271]

Yes Meltdown is not specific to Intel, i don't talk about that. While it is enabled for 64bit, PTI is not enabled also for 32bit x86 OS... there is guy from Suse who is working on it, reaching v6 recently:

https://git.kernel.org/pub/scm/linux...oro/linux.git/

But i don't see that code in regular upstream kernels... well, maybe Suse distro kernels enabling that, no idea there

So, still no idea how could someone asks on kernel mailing list that something which isn't enabled to be disabled

As far as I know. there are several Atom CPUs which are excluded from the PTI and other mitigations for these bugs, at least since 4.16. The ones I remember right now are Pineview and Cedarview Atoms, these ones are already mitigation free (I have a netbook with a n2800 (Cedarview) which has it disabled since that kernel version). It's good to know that they are adding other Atom CPUs to the list. I just bought an old Dell Latitude 2100 with a N270 cpu for $20 so this is quite convenient.

[Girolamo_Cavazzoni]

Isn't Atom N270 32bit only CPU, thus Meltdown mitigation isn't available for these?

If that is true, no idea how could someone asks that something which isn't enabled to be disabled

N270 is one of the few 32-bit only in-order Atoms. Most of its successors are 64-bit.

I should check for any differences on my Dell Mini 1012 after disabling Spectre/Meltdown mitigations...

[mzs.112000]

I disabled Spectre and Meltdown mitigation on my Core 2 Duo laptop (which happens to be my main machine), boot time seems to be much faster, and KDE Plasma starts up faster. This is on Arch Linux with kernel 4.16.11, using an HDD(Not an SSD), and it has 4GB of RAM, CPU is Core 2 Duo P8700
Also, memory usage seems to be unaffected, was 390MB used at startup, is still 390MB used.

[dungeon]

Well, i don't see any code part of upstream kernel releases nor RCs which include Meltdown mitigation for x86 32bit.

I can only conclude that Intel does not care about 32bit, so some distros patching their 32bit kernels with whatever out of tree code... OK, i think i get it now