On 8/30/21 5:39 PM, Andrew David Wong wrote:
On 8/30/21 2:12 PM, haaber wrote:

Kind of answering my own question, but disabling hyperthreading
happened to
be a workaround for the resume from suspend issue.

But shouldn't hyperthreading have already been disabled ever since QSB-043?


I admit that I missed that one as well. Shame on me. Is there some way
to detect active hyperthreading on boot && print out a big red warning ?

That seems a reasonable measure, especially for new-comers how cannot
reasonably be asked to read all old QSB's first :)

I'm confused. I was under the impression that Qubes OS (after the QSB-043 patches) automatically disables hyper-threading for you such that you don't have to know anything, do anything, or read any past QSBs.

As QSB-043 explains, you would have had to follow special instructions to re-enable hyper-threading in Qubes 3.2, and no such instructions were provided for re-enabling it in Qubes 4.0 (since, as the QSB explains, it's never safe in that release), so I don't even know how'd you do it in that release.

But perhaps I'm mistaken or misunderstanding the question.

Ah, a thought just occurred to me. As QSB-043 states, "A CPU
microcode update is required to take advantage of [these patches]." Perhaps the problem is that certain CPUs never received the required microcode updates, which explains why some users seem to have CPUs with hyper-threading enabled even though it's been years since QSB-043. Could that be it?

Of course, it's generally also possible to disable hyper-threading in one's BIOS/EFI settings, regardless of whether it's disabled in Xen, and this does seem like a prudent measure given the risks associated with having it enabled and given the fact that Xen-level disablement appears to be hit-or-miss. So, perhaps your suggestion about detecting and warning about active hyper-threading might be a good idea after all. Please feel free to open an enhancement request.

Andrew David Wong
Community Manager
The Qubes OS Project

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