From: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Sent: Thursday, May 4, 2023 12:03 PM
>
> Implement the validation function which tells the core code whether
> parallel bringup is possible.
>
> The only condition for now is that the kernel does not run in an encrypted
> guest as these will trap the RDMSR via #VC, which cannot be handled at that
> point in early startup.
>
> There was an earlier variant for AMD-SEV which used the GHBC protocol for
> retrieving the APIC ID via CPUID, but there is no guarantee that the
> initial APIC ID in CPUID is the same as the real APIC ID. There is no
> enforcement from the secure firmware and the hypervisor can assign APIC IDs
> as it sees fit as long as the ACPI/MADT table is consistent with that
> assignment.
>
> Unfortunately there is no RDMSR GHCB protocol at the moment, so enabling
> AMD-SEV guests for parallel startup needs some more thought.
>
> Intel-TDX provides a secure RDMSR hypercall, but supporting that is outside
> the scope of this change.
>
> Fixup announce_cpu() as e.g. on Hyper-V CPU1 is the secondary sibling of
> CPU0, which makes the @cpu == 1 logic in announce_cpu() fall apart.
>
> [ mikelley: Reported the announce_cpu() fallout
>
> Originally-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> ---
> V2: Fixup announce_cpu() - Michael Kelley
> ---
> arch/x86/Kconfig | 3 +
> arch/x86/kernel/cpu/common.c | 6 ---
> arch/x86/kernel/smpboot.c | 83 ++++++++++++++++++++++++++++++++++++----
> ---
[snip]
> @@ -934,10 +961,10 @@ static void announce_cpu(int cpu, int ap
> if (!node_width)
> node_width = num_digits(num_possible_nodes()) + 1; /* + '#' */
>
> - if (cpu == 1)
> - printk(KERN_INFO "x86: Booting SMP configuration:\n");
> -
> if (system_state < SYSTEM_RUNNING) {
> + if (num_online_cpus() == 1)
Unfortunately, this new check doesn't work. Here's the output I get:
[ 0.721384] smp: Bringing up secondary CPUs ...
[ 0.725359] smpboot: x86: Booting SMP configuration:
[ 0.729249] .... node #0, CPUs: #2
[ 0.729654] smpboot: x86: Booting SMP configuration:
[ 0.737247] #4
[ 0.737511] smpboot: x86: Booting SMP configuration:
[ 0.741246] #6
[ 0.741508] smpboot: x86: Booting SMP configuration:
[ 0.745248] #8
[ 0.745507] smpboot: x86: Booting SMP configuration:
[ 0.749250] #10
[ 0.749514] smpboot: x86: Booting SMP configuration:
[ 0.753248] #12
[ 0.753492] smpboot: x86: Booting SMP configuration:
[ 0.757249] #14 #1 #3 #5 #7 #9 #11 #13 #15
[ 0.769317] smp: Brought up 1 node, 16 CPUs
[ 0.773246] smpboot: Max logical packages: 1
[ 0.777257] smpboot: Total of 16 processors activated (78253.79 BogoMIPS)
Evidently num_online_cpus() isn't updated until after all the primary
siblings get started.
When booting with cpuhp.parallel=0, the output is good.
Michael
> + pr_info("x86: Booting SMP configuration:\n");
> +
> if (node != current_node) {
> if (current_node > (-1))
> pr_cont("\n");
> @@ -948,7 +975,7 @@ static void announce_cpu(int cpu, int ap
> }
>
> /* Add padding for the BSP */
> - if (cpu == 1)
> + if (num_online_cpus() == 1)
> pr_cont("%*s", width + 1, " ");
>
> pr_cont("%*s#%d", width - num_digits(cpu), " ", cpu);
