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. Use acpi_get_cpu_uid() in pcie_tph_get_cpu_st() to translate from
logical CPU ID to ACPI Processor UID needed for the DSM call.
2. 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."
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 ++--
drivers/pci/tph.c | 16 +++++++++++-----
include/linux/pci-tph.h | 4 ++--
3 files changed, 15 insertions(+), 9 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/drivers/pci/tph.c b/drivers/pci/tph.c
index ca4f97be7538..b67c9ad14bda 100644
--- a/drivers/pci/tph.c
+++ b/drivers/pci/tph.c
@@ -236,21 +236,27 @@ 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
struct pci_dev *rp;
acpi_handle rp_acpi_handle;
union st_info info;
+ u32 cpu_uid;
+ int ret;
+
+ ret = acpi_get_cpu_uid(cpu, &cpu_uid);
+ if (ret != 0)
+ return ret;
rp = pcie_find_root_port(pdev);
if (!rp || !rp->bus || !rp->bus->bridge)
@@ -265,9 +271,9 @@ 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)
--
2.17.1Let's make the subject a little more specific, e.g.,
PCI/TPH: Pass ACPI Processor UID to Cache Locality _DSM
On Thu, Mar 19, 2026 at 02:57:35PM +0800, 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. Use acpi_get_cpu_uid() in pcie_tph_get_cpu_st() to translate from
> logical CPU ID to ACPI Processor UID needed for the DSM call.
> 2. Rename pcie_tpu_get_cpu_st() parameter from cpu_uid to cpu to
> reflect that it is a logical CPU_ID.
And simplify this, e.g.,
pcie_tph_get_cpu_st() uses the Query Cache Locality Features _DSM
[1] to retrieve the TPH Steering Tag for memory associated with the
CPU identified by its "cpu_uid" parameter, a Linux logical CPU ID.
The _DSM requires a ACPI Processor UID, which pcie_tph_get_cpu_st()
previously assumed was the same as the Linux logical CPU ID. This
is true on x86 but not on arm64, so pcie_tph_get_cpu_st() failed on
arm64.
Convert the Linux logical CPU ID to the ACPI Processor UID with
acpi_get_cpu_uid() before passing it to the _DSM.
If there's a specific error message from BNXT or similar that is a
symptom of this problem, it'd be nice to include that. Or if the
problem was just poor performance because the _DSM returned the wrong
Steering Tag, you could say something like:
... so pcie_tph_get_cpu_st() returned the wrong Steering Tag,
resulting in poor network performance.
> [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."
>
> 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>
The patch looks good to me. Thanks for all your work on this!
Reviewed-by: Bjorn Helgaas <bhelgaas@google.com>
> ---
> Documentation/PCI/tph.rst | 4 ++--
> drivers/pci/tph.c | 16 +++++++++++-----
> include/linux/pci-tph.h | 4 ++--
> 3 files changed, 15 insertions(+), 9 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/drivers/pci/tph.c b/drivers/pci/tph.c
> index ca4f97be7538..b67c9ad14bda 100644
> --- a/drivers/pci/tph.c
> +++ b/drivers/pci/tph.c
> @@ -236,21 +236,27 @@ 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
> struct pci_dev *rp;
> acpi_handle rp_acpi_handle;
> union st_info info;
> + u32 cpu_uid;
> + int ret;
> +
> + ret = acpi_get_cpu_uid(cpu, &cpu_uid);
> + if (ret != 0)
> + return ret;
>
> rp = pcie_find_root_port(pdev);
> if (!rp || !rp->bus || !rp->bus->bridge)
> @@ -265,9 +271,9 @@ 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)
> --
> 2.17.1
>
On 3/20/2026 2:32 AM, Bjorn Helgaas wrote:
> Let's make the subject a little more specific, e.g.,
>
> PCI/TPH: Pass ACPI Processor UID to Cache Locality _DSM
done in v10
>
> On Thu, Mar 19, 2026 at 02:57:35PM +0800, 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. Use acpi_get_cpu_uid() in pcie_tph_get_cpu_st() to translate from
>> logical CPU ID to ACPI Processor UID needed for the DSM call.
>> 2. Rename pcie_tpu_get_cpu_st() parameter from cpu_uid to cpu to
>> reflect that it is a logical CPU_ID.
>
> And simplify this, e.g.,
>
> pcie_tph_get_cpu_st() uses the Query Cache Locality Features _DSM
> [1] to retrieve the TPH Steering Tag for memory associated with the
> CPU identified by its "cpu_uid" parameter, a Linux logical CPU ID.
>
> The _DSM requires a ACPI Processor UID, which pcie_tph_get_cpu_st()
> previously assumed was the same as the Linux logical CPU ID. This
> is true on x86 but not on arm64, so pcie_tph_get_cpu_st() failed on
> arm64.
>
> Convert the Linux logical CPU ID to the ACPI Processor UID with
> acpi_get_cpu_uid() before passing it to the _DSM.
>
> If there's a specific error message from BNXT or similar that is a
> symptom of this problem, it'd be nice to include that. Or if the
> problem was just poor performance because the _DSM returned the wrong
> Steering Tag, you could say something like:
>
> ... so pcie_tph_get_cpu_st() returned the wrong Steering Tag,
> resulting in poor network performance.
It is indeed simplified, done in v10
>
>> [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."
>>
>> 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>
>
> The patch looks good to me. Thanks for all your work on this!
>
> Reviewed-by: Bjorn Helgaas <bhelgaas@google.com>
Thanks Bjorn for your review and kind words! I really appreciate it.
>
>> ---
>> Documentation/PCI/tph.rst | 4 ++--
>> drivers/pci/tph.c | 16 +++++++++++-----
>> include/linux/pci-tph.h | 4 ++--
>> 3 files changed, 15 insertions(+), 9 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/drivers/pci/tph.c b/drivers/pci/tph.c
>> index ca4f97be7538..b67c9ad14bda 100644
>> --- a/drivers/pci/tph.c
>> +++ b/drivers/pci/tph.c
>> @@ -236,21 +236,27 @@ 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
>> struct pci_dev *rp;
>> acpi_handle rp_acpi_handle;
>> union st_info info;
>> + u32 cpu_uid;
>> + int ret;
>> +
>> + ret = acpi_get_cpu_uid(cpu, &cpu_uid);
>> + if (ret != 0)
>> + return ret;
>>
>> rp = pcie_find_root_port(pdev);
>> if (!rp || !rp->bus || !rp->bus->bridge)
>> @@ -265,9 +271,9 @@ 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)
>> --
>> 2.17.1
>>
>
© 2016 - 2026 Red Hat, Inc.