Date: Thu, 21 Jun 2018 14:51:51 +0200 From: Lukas Odzioba <lukas.odzioba@...il.com> To: oss-security@...ts.openwall.com Subject: Re: Intel hyper-threading security issues 2018-06-21 13:54 GMT+02:00 Sven Schwedas <sven.schwedas@....at>: > Hotplug doesn't seem differentiate between HT threads and physical > cores, will setting maxcpus=2 on a 2 cores+HT machine reliably disable > HT, or can it disable one core and keep HT active on the other? It depends on machine/BIOS. IIRC usually "non ht" logical cpus are enumerated in in SRAT before ht siblings (kernel goes over this table and boots cpus untill maxcpus is reached), so it will work fine, but I don't think it is standardized in any way. In /proc/cpuinfo among other things you have 1) Linux processor number, 2) apicid 3) core id and the task is to disable minimal number of cpus to make core id unique among those which are online. Of course it doesn't disable HT in any way, just removes certain logical cpus from scheduler. Thanks, Lukas
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