-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 > >>> Marek Marczykowski-Górecki 31.08.2021, 02:52 >>> > On Mon, Aug 30, 2021 at 05:39:40PM -0700, 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? > > > > > > > > https://www.qubes-os.org/news/2018/09/02/qsb-43/ > > > > > > > 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. > > There are (at least) two ways to disable hyper-threading: > 1. In system BIOS (if there is such option) > 2. In software - by disabling every second thread of each core. > > The QSB-043 uses the second method. It has is drawbacks, as the logic to > bring up and down CPUs is quite complex. And yes, there are known > issues[1] affecting suspend. Disabling hyper-threading in BIOS, prevents > Xen from starting those secondary threads at all, and so it doesn't need > to bring them down. > > [1] https://github.com/QubesOS/qubes-issues/issues/6066#issuecomment-901843312
On Fri, Sep 03, 2021 at 10:28:35PM +0200, Ulrich Windl wrote: > Hi! > > > Can't it be disabled via kernel (grub) command line, too? This is exactly "the second method" above. > Also rumours say you can even disable it at runtime (and the threads will be > migrated to other threads before). > Occasionally some tools seem to have problems with HT being disabled (like > "expecting 8 CPUS, but only found 4"). This is kind of similar issue as the one discussed here. That's why it's better to disable HT in BIOS - to not show those 8 CPUs at all. But from the OS level, we don't have other choice, and we prefer a secure default - that's why we disable HT at Xen level, to provide safer option regardless of what user has set in the BIOS. PS Please don't top-post. And keep the mailing list in CC. - -- Best Regards, Marek Marczykowski-Górecki Invisible Things Lab -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhrpukzGPukRmQqkK24/THMrX1ywFAmEylm0ACgkQ24/THMrX 1yxCnwf/UrrViQb+pAT0Ujn5Z3sHVCdUTeYJDXzXBReCEnMfpnIT1OGOyFTNKuoX 2tAFL0WOuXr08GlDbH1UnAebqXjG35wnUPMQYQIerbMgysVi3XcEYk2CaJQwfnnP iMTI5WTe+FFpVgid8JRa8bT38kljELddxufpx7WzvWYfMauab5s+GdB3CeStjP/t cq58mv8d3wGjdRIlHHA8ZX6UXB4REKj+JB9/156H6GiRCeeq5x3bzd9nBOkRAxoX r6yFVwpf3B1mNrtSaz24QRvz5ZUnMFoIB5XSig6xMFghBE+9BvUfcUbhcLWrMlBS 8+UsV/fczd9++e/Atzb6f+S8+e2GyA== =ecZD -----END PGP SIGNATURE----- -- You received this message because you are subscribed to the Google Groups "qubes-users" group. To unsubscribe from this group and stop receiving emails from it, send an email to qubes-users+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/qubes-users/YTKWbX6sqpr8mVCc%40mail-itl.
