X86 January 2018

x86@lists.fedoraproject.org

7 participants
6 discussions

Patches for PTI on x86_32 in review
by Laura Abbott 23 Feb '18

23 Feb '18

Hi, There are now kernel patches for PTI posted for x86_32. If you are interested in this work, it would be very helpful to test and report to the upstream maintainers. https://marc.info/?l=linux-kernel&m=151612149716638 Thanks, Laura

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Multi-byte NOP support on older CPUs
by Florian Weimer 31 Jan '18

31 Jan '18

We are currently emitting additional multi-byte NOPs in Fedora 28, to support the Intel CET feature in future processors. There are some concerns that older CPUs treat these as UD. Pentium Pro and later (i696) are supposed to be fine, but it would be better to double-check. Would those who care about old CPUs please run this test? int main (void) { /* endbr32 */ asm volatile (".byte 0xf3, 0x0f, 0x1e, 0xfb"); /* rdsspd %eax */ asm volatile (".byte 0xf3, 0x0f, 0x1e, 0xc8" ::: "eax"); return 0; } The test passes if running the program does not segfault. You can report he results here or on the redhat-rpm-config bug: https://bugzilla.redhat.com/show_bug.cgi?id=1540591 Thanks, Florian

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Lines of communication: releng, automated testing
by Adam Williamson 31 Jan '18

31 Jan '18

Hi folks! So, the topic of x86 came up in the Fedora panel discussion session at Devconf this week, and one of the aspects we discussed is that there's kind of a lack of lines of communication in a few areas. One especially that I'm interested in is compose quality. It's not unusual for the status of nightly composes (for Branched and Rawhide) to be different on i686 and x86_64. There can be actual arch bugs, or just things like comps differences or lorax behaviour differences or package dependency problems that result in i686 images not building, or failing to work in ways that are arch-specific somehow. When this happens, sometimes myself or Mohan Boddu (mboddu) or Kevin Fenzi (nirik) will notice this, but we don't always have the time/cycles to address it. We have automated testing for nightly composes (and for updates, but at present I'm not running the automated tests on updates) in openQA: https://openqa.fedoraproject.org/ Ideally it'd be great if someone from this group is aware and engaged and involved when some important x86 images are not composing, or x86 tests are failing where x86_64 tests do not. So I wanted to try and open some lines of communication there. Right now, there's a report-y thing run after each compose: https://pagure.io/fedora-qa/check-compose It generates the "compose check report" mails that are sent to devel@. These cover the entire compose, though - so they include x86 information, but it's alongside the x86_64 info and isn't really tailored. It would be possible to tweak check-compose (and the code that runs it) to send an x86-focused report of some kind to this list (or, really, anywhere else), if that would be something people would want. That list could note when important x86 images were missing from the compose, and when there are failed tests which did *not* fail on x86_64, for instance. It doesn't currently have those features, but I'm pretty sure I can add them. So, let me know if that's something folks are interested in, and I can look at doing it. It would also be great on an informal level to just have a known person to poke when x86-specific issues arrive; if there's someone who's usually hanging around in #fedora-releng (most importantly, possibly also #fedora-qa) who we know will care about this sort of thing when poked, that'd go quite a long way to helping, I think. Aside from all the above, I've subscribed to this list and joined #fedora-x86 on Freenode and will do my best to send out feelers when there's a known x86-specific issue. Thanks, folks! -- Adam Williamson Fedora QA Community Monkey IRC: adamw | Twitter: AdamW_Fedora | identi.ca: adamwfedora http://www.happyassassin.net

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Using generic tuning for Fedora i686
by Florian Weimer 25 Jan '18

25 Jan '18

We currently build with -march=i686, which also enables tuning for the original Pentium Pro. This seems to entirely appropriate because even for pure i686 use, most people probably use a Pentium II or a Pentium III or a 32-bit Atom, which have different characters. And of course, most 32-bit users come through x86_64, which are unlikely to benefit from Pentium Pro tuning, either. Should we switch to -march=i686 -mtune=generic instead? Thanks, Florian

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bogus bugs:cpu_meltdown spectre_v1 spectre_v2 in /proc/cpuinfo on i386
by Ralf Corsepius 24 Jan '18

24 Jan '18

Hi, Recent Fedora kernels report # cat /proc/cpuinfo | grep bugs bugs : cpu_meltdown spectre_v1 spectre_v2 on my PIII and my N270s (I.e. all i386ers, I have). To my knowledge, this is entirely bogus. Bug filed: https://bugzilla.redhat.com/show_bug.cgi?id=1537625 Ralf

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KAISER needs to be enabled immediately!
by Subsentient 04 Jan '18

04 Jan '18

Hi, I'm surprised you haven't done so already, but you need to enable kernel/page table isolation in the i686 kernel immediately! i686 is also vulnerable to the Meltdown and Spectre flaws in Intel CPUs, all Intel CPUs past 1995 are! Thanks.

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X86 January 2018