PTI makes my 2 32 bit laptops unstable. I have lubuntu 18.04 installed on both and they both started having trouble after the linux-image upgrade from 4.15.0-46/47 to 4.15.0-50/51. They either fail to boot without locking up or fail to shut down cleanly. I rarely get any useful logs or messages on the screen, although if the machines do boot without locking up, I have seen messages like this when they fail to shut down: watchdog: BUG: soft lockup - CPU#0 stuck for 22s! [systemd:1]
I did manage to recover some BUGs with call traces from kern.log when I tried the ubuntu mainline kernel build, 4.19.31-041931-generic #201903231635. Here are typical BUG stmts: Apr 22 10:16:04 mikedell kernel: [ 43.339955] BUG: unable to handle kernel NULL pointer dereference at 00000008 Apr 22 10:16:04 mikedell kernel: [ 43.484957] BUG: unable to handle kernel paging request at eef4817c Unfortunately, I think it's the only kernel that's given me this much info. I'd be happy to share the full call traces I have captured if anyone is interested. Neither laptop has a serial port and I'm not a kernel developer, so I don't feel I've got the means to properly diagnose the problem. Howver, I have since found that when I compile the kernel from: git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ and change only one config parameter, CONFIG_PAGE_TABLE_ISOLATION, the kernel with the param enabled is unstable, but the kernel with the param disabled is stable. I have found this to be the case with kernels 4.19.50 and 5.1.9. The two laptops are: Dell Inspiron B130 with an Intel Celeron M 1.50GHz (family: 0x6, model: 0xd, stepping: 0x8) IBM Thinkpad R51 1836HAU with Intel Pentium M processor 725 (1.6 GHz) The Thinkpad's Pentium M 725 is a Dothan processor that supports PAE, but lies about it, so it requires the forcepae kernel parameter. The Dell's Celeron M does not requre the forcepae parameter. I've been trying to figure out if this is a known problem. THere's so little love for 32 bt hardware these days. Then I saw this bug report and thought it might be a good place to start. Should I post this info on the linux-kernel mailing list? -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1790688 Title: x86/pti: 32-bit x86 systems support already available. Status in linux package in Ubuntu: Triaged Bug description: Hello. This is a very good news: 'PTI' support for x86-32 architecture is available. Linux kernel v4.19 release candidate, finally have Kernel Page-Table Isolation ('PTI', previously known as 'KAISER') support. As we know, 'PTI' provides protection against attack, known as the "Meltdown" (CVE-2017-5754), that breaks isolation between user applications and the operating system etc. However, this protection - needed for "Meltdown" mitigation - wasn't available on 32-bit x86 systems. Until now. So, I would like to ask a question: are there any plans to backport Kernel Page-Table Isolation patches for Linux kernels available in "Trusty"/14.04, "Xenial"/16.04 and "Bionic"/18.04 releases etc.? I'm asking, because it seems, that pretty much no developers run 32-bit any more. However, there still are many 32-bit users out there. For more informations about how 'PTI' was implemented, created for 32 bit x86 architecture, please check - for example - commit '7757d607c6b31' ("x86/pti: Allow CONFIG_PAGE_TABLE_ISOLATION for x86_32") and these messages on lkml mailing list and lwn.net website (which contains summary of the first half of the 4.19 kernel merge window): ✗ http://lkml.iu.edu/hypermail/linux/kernel/1807.2/02790.html ('PTI' on x86-32; PATCH v.8) ✗ https://lwn.net/Articles/762566/ (See "Architecture-specific" changes) I would like to send a big "Thank You" to Mr Joerg Roedel (and Others, of course) for his amazing work - a whole raft of measures and patches to make this possible - to enable 'PTI' mitigation on x86-32 architecture etc. Thanks, best regards. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1790688/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
