On 2017-05-08 14:34, Jan Kiszka wrote: > On 2017-05-08 13:21, Andy Lutomirski wrote: >> On Mon, May 8, 2017 at 2:32 AM, Andy Shevchenko >> <andy.shevchenko@xxxxxxxxx> wrote: >>> On Mon, May 8, 2017 at 9:31 AM, Jan Kiszka <jan.kiszka@xxxxxxxxxxx> wrote: >>>> On 2017-03-23 10:14, tip-bot for Andy Lutomirski wrote: >>>>> The x86 smpboot trampoline expects initial_page_table to have the >>>>> GDT mapped. If the GDT ends up in a virtually mapped per-cpu page, >>>>> then it won't be in the page tables at all until perc-pu areas are >>>>> set up. The result will be a triple fault the first time that the >>>>> CPU attempts to access the GDT after LGDT loads the perc-pu GDT. >>>>> >>>>> This appears to be an old bug, but somehow the GDT fixmap rework >>>>> is triggering it. This seems to have something to do with the >>>>> memory layout. >>> >>>> This breaks the boot on our Intel Quark platform (IOT2000, similar to >>>> Galileo Gen2). Reverting it over master makes it work again. Any idea >>>> what goes wrong? Let me know how I can help debugging this. >>> >>> JFYI: As of today linux-next when _kexec:ed_ works fine to me >>> >>> Perhaps I can test this later with direct boot from SD card. >>> >> >> The most likely explanation is that there's some code that needs the >> page table synced and runs before setup_per_cpu_areas(). The relevant >> init code is: >> >> setup_arch(&command_line); >> mm_init_cpumask(&init_mm); >> setup_command_line(command_line); >> setup_nr_cpu_ids(); >> setup_per_cpu_areas(); >> >> so I didn't move it very far. It would be awesome if we could get a >> backtrace when the failure happens, but it's likely to be a triple >> fault. Is this an EFI boot? I bet the failure is in efi_init(). > > Yes, it's an EFI thing. Unfortunately, I didn't make > earlycon/earlyprintk work yet. > >> >> Could you try reverting just the deletions in the patch? I.e. try a >> kernel with both the old and the new copies of the code I moved. > > Let me try that later. I can also move the new code around to nail down > the dependency. > I found the reason: your patch is very discriminating! Not the whole world is multicore yet. ;) setup_per_cpu_areas() is taken from mm/percpu.c in case of !CONFIG_SMP. So the new home for the resync is not even built. Any suggestions how to refactor things instead? Jan -- Siemens AG, Corporate Technology, CT RDA ITP SES-DE Corporate Competence Center Embedded Linux -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
