Re: [PATCH v2] x86/apic/of: Fix CPU devicetree-node lookups

[Johan Hovold <johan@kernel.org>]

On Thu, Dec 10, 2020 at 02:39:10PM +0100, Johan Hovold wrote:
> Architectures that describe the CPU topology in devicetree and that do
> not have an identity mapping between physical and logical CPU ids need
> to override the default implementation of arch_match_cpu_phys_id().
> 
> Failing to do so breaks CPU devicetree-node lookups using
> of_get_cpu_node() and of_cpu_device_node_get() which several drivers
> rely on. It also causes the CPU struct devices exported through sysfs to
> point to the wrong devicetree nodes.
> 
> On x86, CPUs are described in devicetree using their APIC ids and those
> do not generally coincide with the logical ids, even if CPU0 typically
> uses APIC id 0. Add the missing implementation of
> arch_match_cpu_phys_id() so that CPU-node lookups work also with SMP.
> 
> Apart from fixing the broken sysfs devicetree-node links this likely do
> not affect users of mainline kernels as the above mentioned drivers are
> currently not used on x86 as far as I know.
> 
> Fixes: 4e07db9c8db8 ("x86/devicetree: Use CPU description from Device Tree")
> Cc: stable <stable@vger.kernel.org>     # 4.17
> Signed-off-by: Johan Hovold <johan@kernel.org>
> ---
> 
> Thomas,
> 
> Hope this looks better to you.
> 
> My use case for this is still out-of-tree, but since CPU-node lookup is
> generic functionality and with observable impact also for mainline users
> (sysfs) I added a stable tag.

Did you have a chance to look at this one yet?

Johan

> Changes in v2
>  - rewrite commit message
>  - add Fixes tag
>  - add stable tag for the benefit of out-of-tree users
> 
> 
>  arch/x86/kernel/apic/apic.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index b3eef1d5c903..19c0119892dd 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -2311,6 +2311,11 @@ static int cpuid_to_apicid[] = {
>  	[0 ... NR_CPUS - 1] = -1,
>  };
>  
> +bool arch_match_cpu_phys_id(int cpu, u64 phys_id)
> +{
> +	return phys_id == cpuid_to_apicid[cpu];
> +}
> +
>  #ifdef CONFIG_SMP
>  /**
>   * apic_id_is_primary_thread - Check whether APIC ID belongs to a primary thread