Re: [PATCH] x86/topology: Fix Hygon logical_die_id by mapping from amd_node_id

[Yazen Ghannam]

On Sun, Mar 01, 2026 at 10:11:56PM +0800, Aichun Shi wrote:
> On Hygon CPUs, for some cases such as EDAC error decoding, contiguous die
> IDs are required. cpuinfo_topology.amd_node_id cannot be used directly as
> it may be non-contiguous, thus cpuinfo_topology.logical_die_id can be used
> in such cases.
> 
> When CPUID leaf 0x80000026 is not available on Hygon CPUs, die (or node)
> topology is not encoded in APIC ID space. logical_die_id obtained from
> topology_get_logical_id(apicid, TOPO_DIE_DOMAIN) therefore does not align
> with die (or node) topology and is incorrect.
> 
> Fix this by adding a Hygon-only fixup in a new topology_hygon.c: Build a
> bijective mapping from (logical_pkg_id, amd_node_id) to a contiguous
> logical_die_id. Leave the original APIC-based path unchanged when CPUID
> leaf 0x80000026 is available.
> 
> Signed-off-by: Aichun Shi <shiaichun@xxxxxxxxxxxxxx>
> ---
>  arch/x86/kernel/cpu/Makefile          |  2 +-
>  arch/x86/kernel/cpu/topology.h        |  5 ++
>  arch/x86/kernel/cpu/topology_common.c |  3 +
>  arch/x86/kernel/cpu/topology_hygon.c  | 86 +++++++++++++++++++++++++++
>  4 files changed, 95 insertions(+), 1 deletion(-)
>  create mode 100644 arch/x86/kernel/cpu/topology_hygon.c
> 
> diff --git a/arch/x86/kernel/cpu/Makefile b/arch/x86/kernel/cpu/Makefile
> index 2f8a58ef690e..4e80d0a5d0c9 100644
> --- a/arch/x86/kernel/cpu/Makefile
> +++ b/arch/x86/kernel/cpu/Makefile
> @@ -38,10 +38,10 @@ obj-y					+= intel.o tsx.o
>  obj-$(CONFIG_PM)			+= intel_epb.o
>  endif
>  obj-$(CONFIG_CPU_SUP_AMD)		+= amd.o
> +obj-$(CONFIG_CPU_SUP_HYGON)		+= hygon.o topology_hygon.o
>  ifeq ($(CONFIG_AMD_NB)$(CONFIG_SYSFS),yy)
>  obj-y					+= amd_cache_disable.o
>  endif
> -obj-$(CONFIG_CPU_SUP_HYGON)		+= hygon.o
>  obj-$(CONFIG_CPU_SUP_CYRIX_32)		+= cyrix.o
>  obj-$(CONFIG_CPU_SUP_CENTAUR)		+= centaur.o
>  obj-$(CONFIG_CPU_SUP_TRANSMETA_32)	+= transmeta.o
> diff --git a/arch/x86/kernel/cpu/topology.h b/arch/x86/kernel/cpu/topology.h
> index 37326297f80c..7203ff0457a4 100644
> --- a/arch/x86/kernel/cpu/topology.h
> +++ b/arch/x86/kernel/cpu/topology.h
> @@ -22,6 +22,11 @@ void topology_set_dom(struct topo_scan *tscan, enum x86_topology_domains dom,
>  bool cpu_parse_topology_ext(struct topo_scan *tscan);
>  void cpu_parse_topology_amd(struct topo_scan *tscan);
>  void cpu_topology_fixup_amd(struct topo_scan *tscan);
> +#ifdef CONFIG_CPU_SUP_HYGON
> +void cpu_topology_fixup_hygon(struct topo_scan *tscan);
> +#else
> +static inline void cpu_topology_fixup_hygon(struct topo_scan *tscan) { }
> +#endif
>  
>  static inline u32 topo_shift_apicid(u32 apicid, enum x86_topology_domains dom)
>  {
> diff --git a/arch/x86/kernel/cpu/topology_common.c b/arch/x86/kernel/cpu/topology_common.c
> index 71625795d711..82803744bd0e 100644
> --- a/arch/x86/kernel/cpu/topology_common.c
> +++ b/arch/x86/kernel/cpu/topology_common.c
> @@ -199,6 +199,9 @@ static void topo_set_ids(struct topo_scan *tscan, bool early)
>  
>  	if (c->x86_vendor == X86_VENDOR_AMD)
>  		cpu_topology_fixup_amd(tscan);
> +
> +	if (c->x86_vendor == X86_VENDOR_HYGON && !early)
> +		cpu_topology_fixup_hygon(tscan);
>  }
>  
>  void cpu_parse_topology(struct cpuinfo_x86 *c)
> diff --git a/arch/x86/kernel/cpu/topology_hygon.c b/arch/x86/kernel/cpu/topology_hygon.c
> new file mode 100644
> index 000000000000..645c30524da6
> --- /dev/null
> +++ b/arch/x86/kernel/cpu/topology_hygon.c
> @@ -0,0 +1,86 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <linux/cpu.h>
> +#include <linux/printk.h>
> +#include <linux/spinlock.h>
> +
> +#include <asm/processor.h>

checkpatch --strict has this:
CHECK: Consider using #include <linux/processor.h> instead of <asm/processor.h>

> +
> +#include "topology.h"
> +
> +/* (logical_pkg_id, amd_node_id) -> logical_die_id mapping. */
> +struct hygon_die_map_entry {
> +	u32 logical_pkg_id;
> +	u32 amd_node_id;
> +	u32 logical_die_id;
> +};
> +
> +static DEFINE_SPINLOCK(hygon_die_map_lock);
> +static struct hygon_die_map_entry hygon_die_map[NR_CPUS];

This is a lot of structures to statically allocate. NR_CPUS can be set
up to 8192.

If you must allocate statically, is there a more conservative value?

For example, the max number of "AMD Nodes" per system is '8'. If the
goal is to map "amd_node_id" to another value, then you will still have
a limit of '8' for the other value.

Also, does amd_num_nodes() still work in this case? I understand that
the "ID" values are not contiguous, but is there still a discoverable
"total number"?

> +static u32 hygon_next_logical_die_id;
> +static unsigned int hygon_die_map_nr;
> +
> +/*
> + * Build a bijective mapping from (logical_pkg_id, amd_node_id) to a contiguous
> + * logical_die_id for Hygon CPUs.
> + *
> + * Returns logical_die_id (>= 0) on success, or -EINVAL on error.

I don't think you need a return value. You can update tscan on success
or leave it on error.

> + */
> +static int hygon_get_logical_die_id(struct topo_scan *tscan)
> +{
> +	struct cpuinfo_x86 *c = tscan->c;
> +	unsigned long flags;
> +	int logical_die_id;
> +	unsigned int i;
> +	int logical_pkg_id = c->topo.logical_pkg_id;
> +
> +	if (c->x86_vendor != X86_VENDOR_HYGON)
> +		return -EINVAL;
> +
> +	if (logical_pkg_id < 0)
> +		return -EINVAL;

Is this possible?

It is 'u32' in 'struct cpuinfo_topology'.

> +
> +	spin_lock_irqsave(&hygon_die_map_lock, flags);
> +
> +	/* Look up existing (logical_pkg_id, amd_node_id) -> logical_die_id. */
> +	for (i = 0; i < hygon_die_map_nr; i++) {
> +		if (hygon_die_map[i].logical_pkg_id == logical_pkg_id &&
> +		    hygon_die_map[i].amd_node_id == tscan->amd_node_id) {
> +			logical_die_id = hygon_die_map[i].logical_die_id;

Just update the 'tscan' data here.

> +			goto out_unlock;
> +		}
> +	}
> +
> +	if (hygon_die_map_nr >= ARRAY_SIZE(hygon_die_map)) {
> +		pr_warn_once("CPU topo: Hygon die map exhausted\n");
> +		logical_die_id = -EINVAL;
> +		goto out_unlock;
> +	}
> +
> +	/* Allocate new contiguous logical_die_id. */
> +	logical_die_id = hygon_next_logical_die_id++;
> +	hygon_die_map[hygon_die_map_nr++] = (struct hygon_die_map_entry) {
> +		.logical_pkg_id = logical_pkg_id,
> +		.amd_node_id = tscan->amd_node_id,
> +		.logical_die_id = logical_die_id,
> +	};
> +
> +out_unlock:
> +	spin_unlock_irqrestore(&hygon_die_map_lock, flags);
> +	return logical_die_id;
> +}
> +
> +void cpu_topology_fixup_hygon(struct topo_scan *tscan)
> +{
> +	/* Skip the fixup if CPUID leaf 0x80000026 is available. */
> +	if (tscan->c->extended_cpuid_level >= 0x80000026)
> +		return;
> +
> +	/* When CPUID leaf 0x80000026 is not available, die (node) topology is

Multi-line comments should start on the next line.

    /*
     * Example
     * comments
     */

> +	 * not encoded in APIC ID space. logical_die_id from the DIE domain is
> +	 * incorrect, so fix it up.
> +	 */
> +	int logical_die_id = hygon_get_logical_die_id(tscan);
> +
> +	if (logical_die_id >= 0)
> +		tscan->c->topo.logical_die_id = logical_die_id;
>

This function could be simpler:

  void cpu_topology_fixup_hygon(struct topo_scan *tscan)
  {
    if (!Hygon)
      return;

    if (CPUID >= 0x80000026)
      return;

    hygon_build_logical_die_id_map(tscan);
  }

Thanks,
Yazen