linux-kernel - RE: [patch V2 38/38] x86/smpboot/64: Implement arch_cpuhp_init_parallel

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Message-ID: <BYAPR21MB168869144087644F89BAC89FD7739@BYAPR21MB1688.namprd21.prod.outlook.com>
Date:   Sat, 6 May 2023 00:53:50 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
CC:     "x86@...nel.org" <x86@...nel.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Brian Gerst <brgerst@...il.com>,
        Arjan van de Veen <arjan@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Paul McKenney <paulmck@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Sean Christopherson <seanjc@...gle.com>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        Paul Menzel <pmenzel@...gen.mpg.de>,
        "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        Piotr Gorski <lucjan.lucjanov@...il.com>,
        Usama Arif <usama.arif@...edance.com>,
        Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
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        Russell King <linux@...linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
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        <linux-arm-kernel@...ts.infradead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Guo Ren <guoren@...nel.org>,
        "linux-csky@...r.kernel.org" <linux-csky@...r.kernel.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
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        Mark Rutland <Mark.Rutland@....com>,
        Sabin Rapan <sabrapan@...zon.com>
Subject: RE: [patch V2 38/38] x86/smpboot/64: Implement
 arch_cpuhp_init_parallel_bringup() and enable it

From: Thomas Gleixner <tglx@...utronix.de> 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@...zon.co.uk>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
> 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);