Core scheduling in 4.1?

Eric · March 28, 2022, 3:51am

I am looking to build another system that needs as many CPU threads as possible (probably AMD Threadripper). I note that Qubes 4.1 uses Xen 4.14 and that core scheduling was introduced into Xen 4.13. Question: is core scheduling supported in Qubes 4.1? It is not mentioned in the 4.1 release notes. Makes most sense to switch to allocating cores instead of CPUs in a qube, since Qubes does not go for high security within a qube, running passwordless root by default.

If not are there any plans?

rustybird · March 28, 2022, 12:07pm

github.com/QubesOS/qubes-issues

Safe use of Hyperthreading when Xen stable includes new sched-gran parameter

opened 09:59PM - 29 Dec 19 UTC

trueriver

T: enhancement C: Xen security P: default

### Qubes OS version: R 4.0.1 All current versions as of 1 Jan 2020 ### Affected component(s) or functionality: Xen, hyperthreading, Intel --- ### Steps to reproduce the behavior: Run Qubes on machine with hyperthreading (HT) hardware ### Expected or desired behavior: HT should ideally be available ### Actual behavior: HT disabled by default ### General notes: HT has been deliberately disabled for security reasons, and with the current relaease versions of Xen this is sensible. The reason is that there exist several exploits on Intel kit that involve abuse of shared cache, etc, when one thread in a CPU is running on one VM and another on another. However, the Xen wizards are on the case, and they have a fix that will ensure that all the threads running on a cpu are allocated together. This means that the only software exposed by such exploits will be software that already has access to that machine. This may reduce the attack surface to an acceptable level for at least some users. The patch is now included in some unstable branches of Xen, and is invoked by the command line parameters smt on sched-gran=core (or socket or cpu). My request is that this is implemented by Qubes, but ONLY once we start using a Xen version that includes this feature. However, it is currently (Jan 2020) too soon to change the current behaviour, as the versions of Xen currently in use ignore this combination without warning. My request therefore is that this is assigned a sensibly long timescale. --- ### I have consulted the following relevant [documentation](https://www.qubes-os.org/doc/): https://www.slideshare.net/xen_com_mgr/xpdds19-core-scheduling-in-xen-jrgen-gro-suse https://patchwork.kernel.org/cover/11086677/ https://xenbits.xen.org/docs/unstable/misc/xen-command-line.html#sched-gran-x86 (NOTE the above path is in the "unstable" branch) ### I am aware of the following related, [non-duplicate](https://www.qubes-os.org/doc/reporting-bugs/#new-issues-should-not-be-duplicates-of-existing-issues) issues:

Eric · March 28, 2022, 10:10pm

Thanks @rustybird the last post says “smt=on sched-gran=core” works in 4.1 - the question is what do you actually get in Qubes? Does vCPU allocation become vCore? Sorry not running 4.1 to test, trying to make an informed decision.
Marek says it will be supported when it is no longer experimental (that was in 4.13 days) are there any updates?