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    SubjectRe: [External] Re: [PATCH v9 0/8] Parallel CPU bringup for x86_64
    On 21.02.2023 21:04, Usama Arif wrote:
    > On 21/02/2023 19:10, David Woodhouse wrote:
    >> On Tue, 2023-02-21 at 13:14 +0100, Oleksandr Natalenko wrote:
    >>>
    >>> With this in place:
    >>>
    >>> ```
    >>>         early_gdt_descr.address = (unsigned long)get_cpu_gdt_rw(0);
    >>>         initial_gs = per_cpu_offset(0);
    >>>         smpboot_control = 0;
    >>> ```
    >>>
    >>> the resume does not work.
    >>
    >> Yeah, I think it's always running on CPU0 after the other CPUs are
    >> taken down anyway.
    >>
    >> We definitely *do* need to clear smpboot_control because we absolutely
    >> want it using the temp_stack we explicitly put into initial_stack, not
    >> finding its own idle thread.
    >>
    >> The problem was that it was never being restored to STARTUP_SECONDARY
    >> in the parallel modes, because that's a one-time setup in
    >> native_smp_prepare_cpus(). So we can just restore it in
    >> arch_thaw_secondary_cpus_begin() too, by working this into patch 6 of
    >> the series.
    >>
    >> (Usama, I think my tree is fairly out of date now so I'll let you do
    >> that? Thanks!).
    >
    > Sounds good! Will send out the next revision with below diff,
    > checkpatch
    > fixes and rebased to 6.2 (testing it now). The below fix looks good!
    > Oleksandr, would you mind testing out suspend/resume with the below
    > diff on your AMD machine just to make sure it fixes the issue before I
    > send out the next revision with it. Thanks!

    Right, so I applied the whole series + this fix, and the suspend/resume
    works. Thanks!

    Reported-by: Oleksandr Natalenko <oleksandr@natalenko.name>
    Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>

    There's another open question pending though: why would this series
    cause booting up one CPU only on an older AMD CPU. But I'd expect
    Piotr's fellow to chime in occasionally.

    >> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
    >> index 50621793671d..3db77a257ae2 100644
    >> --- a/arch/x86/kernel/smpboot.c
    >> +++ b/arch/x86/kernel/smpboot.c
    >> @@ -1571,6 +1571,17 @@ void __init native_smp_prepare_cpus(unsigned
    >> int max_cpus)
    >> void arch_thaw_secondary_cpus_begin(void)
    >> {
    >> + /*
    >> + * On suspend, smpboot_control will have been zeroed to allow the
    >> + * boot CPU to use explicitly passed values including a temporary
    >> + * stack. Since native_smp_prepare_cpus() won't be called again,
    >> + * restore the appropriate value for the parallel startup modes.
    >> + */
    >> + if (do_parallel_bringup) {
    >> + smpboot_control = STARTUP_SECONDARY |
    >> + (x2apic_mode ? STARTUP_APICID_CPUID_0B : STARTUP_APICID_CPUID_01);
    >> + }
    >> +
    >> set_cache_aps_delayed_init(true);
    >> }
    >>

    --
    Oleksandr Natalenko (post-factum)

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