Re: [PATCH v5 2/2] PCI/TPH: Fix get cpu steer-tag fail on ARM64 platform

Jeremy Linton
2026-03-10T15:59:20Z

Hi,

+Wathsala who has been looking at TPH too.

On 3/9/26 10:20 PM, Chengwen Feng wrote:
> pcie_tph_get_cpu_st() is broken on ARM64:
> 1. pcie_tph_get_cpu_st() passes cpu_uid to the PCI ACPI DSM method.
> cpu_uid should be the ACPI Processor UID [1].
> 2. In BNXT, pcie_tph_get_cpu_st() is passed a cpu_uid obtained via
> cpumask_first(irq->cpu_mask) - the logical CPU ID of a CPU core,
> generated and managed by kernel (e.g., [0,255] for a system with 256
> logical CPU cores).
> 3. On ARM64 platforms, ACPI assigns Processor UID to cores listed in the
> MADT table, and this UID may not match the kernel's logical CPU ID.
> When this occurs, the mismatch results in the wrong CPU steer-tag.
> 4. On AMD x86 the logical CPU ID is identical to the ACPI Processor UID
> so the mismatch is not seen.
>
> Resolution:
> 1. Implement acpi_get_cpu_acpi_id() for x86, which replaces
> cpu_acpi_id(). All ACPI platforms now have an implementation.
> 2. Use acpi_get_cpu_acpi_id() in pcie_tph_get_cpu_st() to translate from
> logical CPU ID to ACPI Processor UID needed for the DSM call.
> 3. Rename pcie_tpu_get_cpu_st() parameter from cpu_uid to cpu to
> reflect that it is a logical CPU_ID.
>
> [1] According to ECN_TPH-ST_Revision_20200924
> (https://members.pcisig.com/wg/PCI-SIG/document/15470), the input
> is defined as: "If the target is a processor, then this field
> represents the ACPI Processor UID of the processor as specified in
> the MADT. If the target is a processor container, then this field
> represents the ACPI Processor UID of the processor container as
> specified in the PPTT."

The bit about "processor containers" is not supported by linux yet, and
is potentially a problem worth considering.

The original rename comments from the previous patch versions are on
point, but since they have grown large, i'm going to suggest the x86
rename/shuffle here is also in its own patch seperate from the TPH
specific changes like the arm ones now are.

Thanks for looking after this.

>
> Fixes: d2e8a34876ce ("PCI/TPH: Add Steering Tag support")
> Cc: stable@vger.kernel.org
> Signed-off-by: Chengwen Feng <fengchengwen@huawei.com>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
> ---
> Documentation/PCI/tph.rst | 4 ++--
> arch/x86/include/asm/acpi.h | 2 ++
> arch/x86/include/asm/cpu.h | 1 -
> arch/x86/include/asm/smp.h | 1 -
> arch/x86/kernel/cpu/common.c | 12 ++++++++++++
> arch/x86/xen/enlighten_hvm.c | 4 ++--
> drivers/pci/tph.c | 11 ++++++-----
> include/linux/pci-tph.h | 4 ++--
> 8 files changed, 26 insertions(+), 13 deletions(-)
>
> diff --git a/Documentation/PCI/tph.rst b/Documentation/PCI/tph.rst
> index e8993be64fd6..b6cf22b9bd90 100644
> --- a/Documentation/PCI/tph.rst
> +++ b/Documentation/PCI/tph.rst
> @@ -79,10 +79,10 @@ To retrieve a Steering Tag for a target memory associated with a specific
> CPU, use the following function::
>
> int pcie_tph_get_cpu_st(struct pci_dev *pdev, enum tph_mem_type type,
> - unsigned int cpu_uid, u16 *tag);
> + unsigned int cpu, u16 *tag);
>
> The `type` argument is used to specify the memory type, either volatile
> -or persistent, of the target memory. The `cpu_uid` argument specifies the
> +or persistent, of the target memory. The `cpu` argument specifies the
> CPU where the memory is associated to.
>
> After the ST value is retrieved, the device driver can use the following
> diff --git a/arch/x86/include/asm/acpi.h b/arch/x86/include/asm/acpi.h
> index a03aa6f999d1..b968369715c1 100644
> --- a/arch/x86/include/asm/acpi.h
> +++ b/arch/x86/include/asm/acpi.h
> @@ -157,6 +157,8 @@ static inline bool acpi_has_cpu_in_madt(void)
> return !!acpi_lapic;
> }
>
> +u32 acpi_get_cpu_acpi_id(unsigned int cpu);
> +
> #define ACPI_HAVE_ARCH_SET_ROOT_POINTER
> static __always_inline void acpi_arch_set_root_pointer(u64 addr)
> {
> diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
> index ad235dda1ded..57a0786dfd75 100644
> --- a/arch/x86/include/asm/cpu.h
> +++ b/arch/x86/include/asm/cpu.h
> @@ -11,7 +11,6 @@
>
> #ifndef CONFIG_SMP
> #define cpu_physical_id(cpu) boot_cpu_physical_apicid
> -#define cpu_acpi_id(cpu) 0
> #endif /* CONFIG_SMP */
>
> #ifdef CONFIG_HOTPLUG_CPU
> diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
> index 84951572ab81..05d1d479b4cf 100644
> --- a/arch/x86/include/asm/smp.h
> +++ b/arch/x86/include/asm/smp.h
> @@ -130,7 +130,6 @@ __visible void smp_call_function_interrupt(struct pt_regs *regs);
> __visible void smp_call_function_single_interrupt(struct pt_regs *r);
>
> #define cpu_physical_id(cpu) per_cpu(x86_cpu_to_apicid, cpu)
> -#define cpu_acpi_id(cpu) per_cpu(x86_cpu_to_acpiid, cpu)
>
> /*
> * This function is needed by all SMP systems. It must _always_ be valid
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index 1c3261cae40c..93f4f3283c81 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -29,6 +29,7 @@
> #include <linux/utsname.h>
> #include <linux/efi.h>
>
> +#include <asm/acpi.h>
> #include <asm/alternative.h>
> #include <asm/cmdline.h>
> #include <asm/cpuid/api.h>
> @@ -57,6 +58,7 @@
> #include <asm/asm.h>
> #include <asm/bugs.h>
> #include <asm/cpu.h>
> +#include <asm/smp.h>
> #include <asm/mce.h>
> #include <asm/msr.h>
> #include <asm/cacheinfo.h>
> @@ -2643,3 +2645,13 @@ void __init arch_cpu_finalize_init(void)
> */
> mem_encrypt_init();
> }
> +
> +u32 acpi_get_cpu_acpi_id(unsigned int cpu)
> +{
> +#ifndef CONFIG_SMP
> + return 0;
> +#else
> + return per_cpu(x86_cpu_to_acpiid, cpu);
> +#endif
> +}
> +EXPORT_SYMBOL_GPL(acpi_get_cpu_acpi_id);
> diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c
> index fe57ff85d004..0a5cde7865b2 100644
> --- a/arch/x86/xen/enlighten_hvm.c
> +++ b/arch/x86/xen/enlighten_hvm.c
> @@ -161,8 +161,8 @@ static int xen_cpu_up_prepare_hvm(unsigned int cpu)
> */
> xen_uninit_lock_cpu(cpu);
>
> - if (cpu_acpi_id(cpu) != CPU_ACPIID_INVALID)
> - per_cpu(xen_vcpu_id, cpu) = cpu_acpi_id(cpu);
> + if (acpi_get_cpu_acpi_id(cpu) != CPU_ACPIID_INVALID)
> + per_cpu(xen_vcpu_id, cpu) = acpi_get_cpu_acpi_id(cpu);
> else
> per_cpu(xen_vcpu_id, cpu) = cpu;
> xen_vcpu_setup(cpu);
> diff --git a/drivers/pci/tph.c b/drivers/pci/tph.c
> index ca4f97be7538..c1bd60637b5a 100644
> --- a/drivers/pci/tph.c
> +++ b/drivers/pci/tph.c
> @@ -236,18 +236,19 @@ static int write_tag_to_st_table(struct pci_dev *pdev, int index, u16 tag)
> * with a specific CPU
> * @pdev: PCI device
> * @mem_type: target memory type (volatile or persistent RAM)
> - * @cpu_uid: associated CPU id
> + * @cpu: associated CPU id
> * @tag: Steering Tag to be returned
> *
> * Return the Steering Tag for a target memory that is associated with a
> - * specific CPU as indicated by cpu_uid.
> + * specific CPU as indicated by cpu.
> *
> * Return: 0 if success, otherwise negative value (-errno)
> */
> int pcie_tph_get_cpu_st(struct pci_dev *pdev, enum tph_mem_type mem_type,
> - unsigned int cpu_uid, u16 *tag)
> + unsigned int cpu, u16 *tag)
> {
> #ifdef CONFIG_ACPI
> + u32 cpu_uid = acpi_get_cpu_acpi_id(cpu);
> struct pci_dev *rp;
> acpi_handle rp_acpi_handle;
> union st_info info;
> @@ -265,9 +266,9 @@ int pcie_tph_get_cpu_st(struct pci_dev *pdev, enum tph_mem_type mem_type,
>
> *tag = tph_extract_tag(mem_type, pdev->tph_req_type, &info);
>
> - pci_dbg(pdev, "get steering tag: mem_type=%s, cpu_uid=%d, tag=%#04x\n",
> + pci_dbg(pdev, "get steering tag: mem_type=%s, cpu=%d, tag=%#04x\n",
> (mem_type == TPH_MEM_TYPE_VM) ? "volatile" : "persistent",
> - cpu_uid, *tag);
> + cpu, *tag);
>
> return 0;
> #else
> diff --git a/include/linux/pci-tph.h b/include/linux/pci-tph.h
> index ba28140ce670..be68cd17f2f8 100644
> --- a/include/linux/pci-tph.h
> +++ b/include/linux/pci-tph.h
> @@ -25,7 +25,7 @@ int pcie_tph_set_st_entry(struct pci_dev *pdev,
> unsigned int index, u16 tag);
> int pcie_tph_get_cpu_st(struct pci_dev *dev,
> enum tph_mem_type mem_type,
> - unsigned int cpu_uid, u16 *tag);
> + unsigned int cpu, u16 *tag);
> void pcie_disable_tph(struct pci_dev *pdev);
> int pcie_enable_tph(struct pci_dev *pdev, int mode);
> u16 pcie_tph_get_st_table_size(struct pci_dev *pdev);
> @@ -36,7 +36,7 @@ static inline int pcie_tph_set_st_entry(struct pci_dev *pdev,
> { return -EINVAL; }
> static inline int pcie_tph_get_cpu_st(struct pci_dev *dev,
> enum tph_mem_type mem_type,
> - unsigned int cpu_uid, u16 *tag)
> + unsigned int cpu, u16 *tag)
> { return -EINVAL; }
> static inline void pcie_disable_tph(struct pci_dev *pdev) { }
> static inline int pcie_enable_tph(struct pci_dev *pdev, int mode)