Re: [PATCH v1 1/1] tpm: tpm_crb_ffa: Only register driver when ACPI TPM2 uses FF-A

[Jarkko Sakkinen <jarkko@kernel.org>]

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On Thu, Nov 12, 2026 at 11:38:07PM +0000, Siddharth Chintamaneni wrote:
> Prior to commit 677042afb97a ("tpm: tpm_crb_ffa: revert defered_probed
> when tpm_crb_ffa is built-in"), built-in tpm_crb_ffa only registered
> tpm_crb_ffa_driver from tpm_crb_ffa_init() after crb_acpi_probe()
> confirmed start_method == ACPI_TPM2_CRB_WITH_ARM_FFA. After that
> commit, tpm_crb_ffa unconditionally registers on the FF-A bus at
> device_initcall time (and when loaded as a module) without checking
> the platform's ACPI TPM2 table.
> 
> A platform's firmware may expose a TPM CRB over FF-A Secure Partition
> for UEFI boot services while advertising a non-FF-A start method to
> the OS in the ACPI TPM2 table. When the ACPI TPM2 table designates a
> non-FF-A start method, Linux has no consumer for tpm_crb_ffa and
> should not probe the FF-A TPM service.
> 
> On Microsoft Cobalt 200 systems, the ACPI TPM2 table does not use
> ACPI_TPM2_CRB_WITH_ARM_FFA, yet ffa_init() discovers the FF-A TPM
> partition and tpm_crb_ffa_probe() unconditionally sends
> CRB_FFA_GET_INTERFACE_VERSION via FFA_MSG_SEND_DIRECT_REQ2/REQ SMC.
> That request wedges the calling CPU in Secure World (with Non-Secure
> interrupts and GICv3 pseudo-NMIs masked), hanging boot with an RCU CPU
> stall:
> 
>   [    5.507519] ARM FF-A: Driver version 1.2
>   [    5.507519] ARM FF-A: Firmware version 1.2 found
>   [    5.507551] ARM FF-A: Notification setup failed -61, not enabled
>   [    7.150580] Freeing initrd memory: 293640K
>   [   65.515248] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
>   [   65.521346] rcu:     10-...0: (3 GPs behind) idle=dd9c/1/0x4000000000000000 softirq=37/37 fqs=5262
>   [   65.530031] rcu:              hardirqs   softirqs   csw/system
>   [   65.535589] rcu:      number:        0          0            0
>   [   65.541146] rcu:     cputime:        0          0            0   ==> 30028(ms)
>   [   65.548102] rcu:     (detected by 66, t=15010 jiffies, g=-951, q=1384 ncpus=132)
>   [   65.555228] Sending NMI from CPU 66 to CPUs 10:
>   [   75.560686] After 10 seconds, these CPUS still haven't responded to the NMI: 10
> 
> Check the ACPI TPM2 table in tpm_crb_ffa_driver_init() and return
> -ENODEV before calling ffa_register() unless the table is present and
> specifies ACPI_TPM2_CRB_WITH_ARM_FFA, matching the check_acpi_tpm2()
> pattern in tpm_tis.c. This ensures Linux only issues FF-A TPM requests
>
> when ACPI advertises the FF-A start method (for both built-in and
> modular builds), while preserving normal FF-A bus probing on platforms
> that use CRB over FF-A.
> 
> Fixes: 677042afb97a ("tpm: tpm_crb_ffa: revert defered_probed when tpm_crb_ffa is built-in")
> Fixes: eb93f0734ef1 ("tpm_crb: ffa_tpm: Implement driver compliant to CRB over FF-A")

Pick the older.

I attached a prepending patch that caches the start method, which can be
later used in tpm_tis and tpm_crb.

So that totals four patches:

1. My patch.
2. Your fix using the cached value.
3. tpm_tis update to use the cached value.
4. tpm_crb update to use the cached value.

Fast-forward when these are in the mainline, I can send my change with
Stable-dep-of tag to stable@vger.kernel.org.

Br, Jarkko

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From fc841edc9b4036bed36126dbdc7fdd41cee185c8 Mon Sep 17 00:00:00 2001
From: Jarkko Sakkinen <jarkko@kernel.org>
Date: Fri, 13 Nov 2026 20:18:42 +0200
Subject: [PATCH] tpm: Cache TPM2 start method

Both tpm_tis and tpm_crb have duplicate code for retrieving the start
method from TPM2 ACPI table. Eagerly cache the start method already at chip
creation. The cached chip->start_method can then be used by the leaf
drivers; or ignored depending on the requirements.

Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
---
 drivers/char/tpm/tpm-chip.c | 36 +++++++++++++++++++++++++++++-------
 include/linux/tpm.h         |  1 +
 2 files changed, 30 insertions(+), 7 deletions(-)

diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
index 0be5dbfaa72e..540dd366effc 100644
--- a/drivers/char/tpm/tpm-chip.c
+++ b/drivers/char/tpm/tpm-chip.c
@@ -256,18 +256,24 @@ int tpm_class_shutdown(struct device *dev)
 }
 
 /**
- * tpm_chip_alloc() - allocate a new struct tpm_chip instance
- * @pdev: device to which the chip is associated
- *        At this point pdev mst be initialized, but does not have to
- *        be registered
- * @ops: struct tpm_class_ops instance
+ * tpm_chip_alloc() - Allocate a new struct tpm_chip instance
+ * @pdev:	device to which the chip is associated At this point pdev mst be
+ *		initialized, but does not have to be registered
+ * @ops:	struct tpm_class_ops for the chip.
+ *
+ * Allocates a new struct tpm_chip instance, and assigns a free device number
+ * for it. Must be paired with put_device(&chip->dev).
  *
- * Allocates a new struct tpm_chip instance and assigns a free
- * device number for it. Must be paired with put_device(&chip->dev).
+ * When ACPI is enabled, additionally tries to eagerly cache the start method
+ * from TPM2 ACPI table for the devices that need know it.
  */
 struct tpm_chip *tpm_chip_alloc(struct device *pdev,
 				const struct tpm_class_ops *ops)
 {
+#ifdef CONFIG_ACPI
+	struct acpi_table_tpm2 *tbl;
+	acpi_status status;
+#endif
 	struct tpm_chip *chip;
 	int rc;
 
@@ -275,6 +281,22 @@ struct tpm_chip *tpm_chip_alloc(struct device *pdev,
 	if (chip == NULL)
 		return ERR_PTR(-ENOMEM);
 
+#ifdef CONFIG_ACPI
+	chip->start_method = ACPI_TPM2_NOT_ALLOWED;
+	if (!acpi_disabled) {
+		status = acpi_get_table(ACPI_SIG_TPM2, 1, (struct acpi_table_header **)&tbl);
+		if (!ACPI_FAILURE(status) || tbl->header.length >= sizeof(*tbl)) {
+			chip->start_method = tbl->start_method;
+			dev_info(pdev, "TPM2 ACPI table is available");
+		} else {
+			dev_info(pdev, "TPM2 ACPI table is not available");
+		}
+
+		if (!ACPI_FAILURE(status))
+			acpi_put_table((struct acpi_table_header *)tbl);
+	}
+#endif
+
 	mutex_init(&chip->tpm_mutex);
 	init_rwsem(&chip->ops_sem);
 
diff --git a/include/linux/tpm.h b/include/linux/tpm.h
index 0db277af45c3..f6cc91615469 100644
--- a/include/linux/tpm.h
+++ b/include/linux/tpm.h
@@ -149,6 +149,7 @@ struct tpm_chip {
 	struct tpm_bank_info allocated_banks[TPM2_MAX_PCR_BANKS];
 #ifdef CONFIG_ACPI
 	acpi_handle acpi_dev_handle;
+	u32 start_method;
 	char ppi_version[TPM_PPI_VERSION_LEN + 1];
 #endif /* CONFIG_ACPI */
 
-- 
2.47.3