Re: [patch v3 31/36] x86/apic: Provide cpu_primary_thread mask

Kirill A. Shutemov
2023-05-24T20:48:56Z

On Mon, May 08, 2023 at 09:44:17PM +0200, Thomas Gleixner wrote:
> From: Thomas Gleixner <tglx@linutronix.de>
>
> Make the primary thread tracking CPU mask based in preparation for simpler
> handling of parallel bootup.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Tested-by: Michael Kelley <mikelley@microsoft.com>
>
>
> ---
> arch/x86/include/asm/apic.h | 2 --
> arch/x86/include/asm/topology.h | 19 +++++++++++++++----
> arch/x86/kernel/apic/apic.c | 20 +++++++++-----------
> arch/x86/kernel/smpboot.c | 12 +++---------
> 4 files changed, 27 insertions(+), 26 deletions(-)
> ---
>

...

> @@ -2386,20 +2386,16 @@ bool arch_match_cpu_phys_id(int cpu, u64
> }
>
> #ifdef CONFIG_SMP
> -/**
> - * apic_id_is_primary_thread - Check whether APIC ID belongs to a primary thread
> - * @apicid: APIC ID to check
> - */
> -bool apic_id_is_primary_thread(unsigned int apicid)
> +static void cpu_mark_primary_thread(unsigned int cpu, unsigned int apicid)
> {
> - u32 mask;
> -
> - if (smp_num_siblings == 1)
> - return true;
> /* Isolate the SMT bit(s) in the APICID and check for 0 */
> - mask = (1U << (fls(smp_num_siblings) - 1)) - 1;
> - return !(apicid & mask);
> + u32 mask = (1U << (fls(smp_num_siblings) - 1)) - 1;
> +
> + if (smp_num_siblings == 1 || !(apicid & mask))
> + cpumask_set_cpu(cpu, &__cpu_primary_thread_mask);
> }
> +#else
> +static inline void cpu_mark_primary_thread(unsigned int cpu, unsigned int apicid) { }
> #endif
>
> /*

This patch causes boot regression on TDX guest. The guest crashes on SMP
bring up.

The change makes use of smp_num_siblings earlier than before: the mask get
constructed in acpi_boot_init() codepath. Later on smp_num_siblings gets
updated in detect_ht().

In my setup with 16 vCPUs, smp_num_siblings is 16 before detect_ht() and
set to 1 in detect_ht().

--
Kiryl Shutsemau / Kirill A. Shutemov