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Message-ID: <a9c6e8b2-ddd4-4bf9-bbe4-a6a691837672@arm.com>
Date: Wed, 25 Jun 2025 14:09:50 -0500
From: Prachotan Bathi <prachotan.bathi@....com>
To: Jarkko Sakkinen <jarkko@...nel.org>
Cc: Peter Huewe <peterhuewe@....de>, Jason Gunthorpe <jgg@...pe.ca>,
Stuart Yoder <stuart.yoder@....com>, linux-integrity@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 2/2] tpm_crb_ffa: handle tpm busy return code
On 6/24/25 6:21 PM, Jarkko Sakkinen wrote:
> On Tue, Jun 17, 2025 at 11:05:44AM -0500, Prachotan Bathi wrote:
>> Platforms supporting direct message request v2 [1] can support secure
>> partitions that support multiple services. For CRB over FF-A interface,
>> if the firmware TPM or TPM service [1] shares its Secure Partition (SP)
>> with another service, message requests may fail with a -EBUSY error.
>>
>> To handle this, replace the single check and call with a retry loop
>> that attempts the TPM message send operation until it succeeds or a
>> configurable timeout is reached. Implement a _try_send_receive function
>> to do a single send/receive and modify the existing send_receive to
>> add this retry loop.
>> The retry mechanism introduces a module parameter (`busy_timeout_ms`,
>> default: 2000ms) to control how long to keep retrying on -EBUSY
>> responses. Between retries, the code waits briefly (50-100 microseconds)
>> to avoid busy-waiting and handling TPM BUSY conditions more gracefully.
>>
>> The parameter can be modified at run-time as such:
>> echo 3000 | tee /sys/module/tpm_crb_ffa/parameters/busy_timeout_ms
>> This changes the timeout from the default 2000ms to 3000ms.
>>
>> [1] TPM Service Command Response Buffer Interface Over FF-A
>> https://developer.arm.com/documentation/den0138/latest/
>>
>> Signed-off-by: Prachotan Bathi <prachotan.bathi@....com>
>> ---
>> drivers/char/tpm/tpm_crb_ffa.c | 66 +++++++++++++++++++++++++++-------
>> 1 file changed, 53 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/char/tpm/tpm_crb_ffa.c b/drivers/char/tpm/tpm_crb_ffa.c
>> index 089d1e54bb46..4615347795fa 100644
>> --- a/drivers/char/tpm/tpm_crb_ffa.c
>> +++ b/drivers/char/tpm/tpm_crb_ffa.c
>> @@ -10,8 +10,12 @@
>> #define pr_fmt(fmt) "CRB_FFA: " fmt
>>
>> #include <linux/arm_ffa.h>
>> +#include <linux/delay.h>
>> +#include <linux/moduleparam.h>
>> #include "tpm_crb_ffa.h"
>>
>> +#define memzero(s, n) memset((s), 0, (n))
>> +
>> /* TPM service function status codes */
>> #define CRB_FFA_OK 0x05000001
>> #define CRB_FFA_OK_RESULTS_RETURNED 0x05000002
>> @@ -178,22 +182,18 @@ int tpm_crb_ffa_init(void)
>> }
>> EXPORT_SYMBOL_GPL(tpm_crb_ffa_init);
>>
>> -static int __tpm_crb_ffa_send_receive(unsigned long func_id,
>> - unsigned long a0,
>> - unsigned long a1,
>> - unsigned long a2)
>> +static int __tpm_crb_ffa_try_send_receive(unsigned long func_id,
>> + unsigned long a0, unsigned long a1,
>> + unsigned long a2)
>> {
>> const struct ffa_msg_ops *msg_ops;
>> int ret;
>>
>> - if (!tpm_crb_ffa)
>> - return -ENOENT;
>> -
>> msg_ops = tpm_crb_ffa->ffa_dev->ops->msg_ops;
>>
>> if (ffa_partition_supports_direct_req2_recv(tpm_crb_ffa->ffa_dev)) {
>> - memset(&tpm_crb_ffa->direct_msg_data2, 0x00,
>> - sizeof(struct ffa_send_direct_data2));
>> + memzero(&tpm_crb_ffa->direct_msg_data2,
>> + sizeof(struct ffa_send_direct_data2));
>>
>> tpm_crb_ffa->direct_msg_data2.data[0] = func_id;
>> tpm_crb_ffa->direct_msg_data2.data[1] = a0;
>> @@ -201,12 +201,12 @@ static int __tpm_crb_ffa_send_receive(unsigned long func_id,
>> tpm_crb_ffa->direct_msg_data2.data[3] = a2;
>>
>> ret = msg_ops->sync_send_receive2(tpm_crb_ffa->ffa_dev,
>> - &tpm_crb_ffa->direct_msg_data2);
>> + &tpm_crb_ffa->direct_msg_data2);
>> if (!ret)
>> ret = tpm_crb_ffa_to_linux_errno(tpm_crb_ffa->direct_msg_data2.data[0]);
>> } else {
>> - memset(&tpm_crb_ffa->direct_msg_data, 0x00,
>> - sizeof(struct ffa_send_direct_data));
>> + memzero(&tpm_crb_ffa->direct_msg_data,
>> + sizeof(struct ffa_send_direct_data));
>>
>> tpm_crb_ffa->direct_msg_data.data1 = func_id;
>> tpm_crb_ffa->direct_msg_data.data2 = a0;
>> @@ -214,11 +214,51 @@ static int __tpm_crb_ffa_send_receive(unsigned long func_id,
>> tpm_crb_ffa->direct_msg_data.data4 = a2;
>>
>> ret = msg_ops->sync_send_receive(tpm_crb_ffa->ffa_dev,
>> - &tpm_crb_ffa->direct_msg_data);
>> + &tpm_crb_ffa->direct_msg_data);
>> if (!ret)
>> ret = tpm_crb_ffa_to_linux_errno(tpm_crb_ffa->direct_msg_data.data1);
>> }
>>
>> + return ret;
>> +}
>> +
>> +static unsigned int busy_timeout_ms = 2000;
>> +/**
>> + * busy_timeout_ms - Maximum time to retry before giving up on busy
> nit: s/busy_timeout_ms/busy_timeout_ms()/
>
>> + *
>> + * This parameter defines the maximum time in milliseconds to retry
>> + * sending a message to the TPM service before giving up.
>> + */
>> +module_param(busy_timeout_ms, uint, 0644);
>> +MODULE_PARM_DESC(busy_timeout_ms,
>> + "Maximum time(in ms) to retry before giving up on busy");
> Patch lacks update to Documentation/admin-guide/kernel-parameters.rst
> (and also document that the default value is two seconds).
>
>> +
>> +static int __tpm_crb_ffa_send_receive(unsigned long func_id, unsigned long a0,
>> + unsigned long a1, unsigned long a2)
>> +{
>> + ktime_t start, stop;
>> + int ret;
>> +
>> + if (!tpm_crb_ffa)
>> + return -ENOENT;
>> +
>> + start = ktime_get();
>> + stop = ktime_add(start, ms_to_ktime(busy_timeout_ms));
>> +
>> + for (;;) {
>> + ret = __tpm_crb_ffa_try_send_receive(func_id, a0, a1, a2);
>> +
>> + if (ret == -EBUSY) {
> This loop would be less convoluted if you instead:
>
> if (ret != -EBUSY)
> break;
>
> /* ... */
>
>> + usleep_range(50, 100);
> I wonder where this range comes from.
This range comes from a similar timeout defined in the
crb_wait_for_reg_32 function.
See:
https://github.com/torvalds/linux/blob/c4dce0c094a89b1bc8fde1163342bd6fe29c0370/drivers/char/tpm/tpm_crb.c#L153
A TPM Service might have a discrete TPM (dtpm) that it communicates
with, a busy SP might become available again and be able to proxy
commands to a dtpm within a similar retry window. This window works well
with current internal implementations and can be changed as future
implementations and specifications evolve and define a more
sophisticated retry window.
>> + if (ktime_after(ktime_get(), stop)) {
>> + dev_warn(&tpm_crb_ffa->ffa_dev->dev,
>> + "Busy retry timed out\n");
>> + break;
>> + }
>> + } else {
>> + break;
>> + }
>> + }
>>
>> return ret;
>> }
>> --
>> 2.43.0
>>
> BR, Jarkko
On 6/24/25 6:21 PM, Jarkko Sakkinen wrote:
> On Tue, Jun 17, 2025 at 11:05:44AM -0500, Prachotan Bathi wrote:
>> Platforms supporting direct message request v2 [1] can support secure
>> partitions that support multiple services. For CRB over FF-A interface,
>> if the firmware TPM or TPM service [1] shares its Secure Partition (SP)
>> with another service, message requests may fail with a -EBUSY error.
>>
>> To handle this, replace the single check and call with a retry loop
>> that attempts the TPM message send operation until it succeeds or a
>> configurable timeout is reached. Implement a _try_send_receive function
>> to do a single send/receive and modify the existing send_receive to
>> add this retry loop.
>> The retry mechanism introduces a module parameter (`busy_timeout_ms`,
>> default: 2000ms) to control how long to keep retrying on -EBUSY
>> responses. Between retries, the code waits briefly (50-100 microseconds)
>> to avoid busy-waiting and handling TPM BUSY conditions more gracefully.
>>
>> The parameter can be modified at run-time as such:
>> echo 3000 | tee /sys/module/tpm_crb_ffa/parameters/busy_timeout_ms
>> This changes the timeout from the default 2000ms to 3000ms.
>>
>> [1] TPM Service Command Response Buffer Interface Over FF-A
>> https://developer.arm.com/documentation/den0138/latest/
>>
>> Signed-off-by: Prachotan Bathi <prachotan.bathi@....com>
>> ---
>> drivers/char/tpm/tpm_crb_ffa.c | 66 +++++++++++++++++++++++++++-------
>> 1 file changed, 53 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/char/tpm/tpm_crb_ffa.c b/drivers/char/tpm/tpm_crb_ffa.c
>> index 089d1e54bb46..4615347795fa 100644
>> --- a/drivers/char/tpm/tpm_crb_ffa.c
>> +++ b/drivers/char/tpm/tpm_crb_ffa.c
>> @@ -10,8 +10,12 @@
>> #define pr_fmt(fmt) "CRB_FFA: " fmt
>>
>> #include <linux/arm_ffa.h>
>> +#include <linux/delay.h>
>> +#include <linux/moduleparam.h>
>> #include "tpm_crb_ffa.h"
>>
>> +#define memzero(s, n) memset((s), 0, (n))
>> +
>> /* TPM service function status codes */
>> #define CRB_FFA_OK 0x05000001
>> #define CRB_FFA_OK_RESULTS_RETURNED 0x05000002
>> @@ -178,22 +182,18 @@ int tpm_crb_ffa_init(void)
>> }
>> EXPORT_SYMBOL_GPL(tpm_crb_ffa_init);
>>
>> -static int __tpm_crb_ffa_send_receive(unsigned long func_id,
>> - unsigned long a0,
>> - unsigned long a1,
>> - unsigned long a2)
>> +static int __tpm_crb_ffa_try_send_receive(unsigned long func_id,
>> + unsigned long a0, unsigned long a1,
>> + unsigned long a2)
>> {
>> const struct ffa_msg_ops *msg_ops;
>> int ret;
>>
>> - if (!tpm_crb_ffa)
>> - return -ENOENT;
>> -
>> msg_ops = tpm_crb_ffa->ffa_dev->ops->msg_ops;
>>
>> if (ffa_partition_supports_direct_req2_recv(tpm_crb_ffa->ffa_dev)) {
>> - memset(&tpm_crb_ffa->direct_msg_data2, 0x00,
>> - sizeof(struct ffa_send_direct_data2));
>> + memzero(&tpm_crb_ffa->direct_msg_data2,
>> + sizeof(struct ffa_send_direct_data2));
>>
>> tpm_crb_ffa->direct_msg_data2.data[0] = func_id;
>> tpm_crb_ffa->direct_msg_data2.data[1] = a0;
>> @@ -201,12 +201,12 @@ static int __tpm_crb_ffa_send_receive(unsigned long func_id,
>> tpm_crb_ffa->direct_msg_data2.data[3] = a2;
>>
>> ret = msg_ops->sync_send_receive2(tpm_crb_ffa->ffa_dev,
>> - &tpm_crb_ffa->direct_msg_data2);
>> + &tpm_crb_ffa->direct_msg_data2);
>> if (!ret)
>> ret = tpm_crb_ffa_to_linux_errno(tpm_crb_ffa->direct_msg_data2.data[0]);
>> } else {
>> - memset(&tpm_crb_ffa->direct_msg_data, 0x00,
>> - sizeof(struct ffa_send_direct_data));
>> + memzero(&tpm_crb_ffa->direct_msg_data,
>> + sizeof(struct ffa_send_direct_data));
>>
>> tpm_crb_ffa->direct_msg_data.data1 = func_id;
>> tpm_crb_ffa->direct_msg_data.data2 = a0;
>> @@ -214,11 +214,51 @@ static int __tpm_crb_ffa_send_receive(unsigned long func_id,
>> tpm_crb_ffa->direct_msg_data.data4 = a2;
>>
>> ret = msg_ops->sync_send_receive(tpm_crb_ffa->ffa_dev,
>> - &tpm_crb_ffa->direct_msg_data);
>> + &tpm_crb_ffa->direct_msg_data);
>> if (!ret)
>> ret = tpm_crb_ffa_to_linux_errno(tpm_crb_ffa->direct_msg_data.data1);
>> }
>>
>> + return ret;
>> +}
>> +
>> +static unsigned int busy_timeout_ms = 2000;
>> +/**
>> + * busy_timeout_ms - Maximum time to retry before giving up on busy
> nit: s/busy_timeout_ms/busy_timeout_ms()/
>
>> + *
>> + * This parameter defines the maximum time in milliseconds to retry
>> + * sending a message to the TPM service before giving up.
>> + */
>> +module_param(busy_timeout_ms, uint, 0644);
>> +MODULE_PARM_DESC(busy_timeout_ms,
>> + "Maximum time(in ms) to retry before giving up on busy");
> Patch lacks update to Documentation/admin-guide/kernel-parameters.rst
> (and also document that the default value is two seconds).
>
>> +
>> +static int __tpm_crb_ffa_send_receive(unsigned long func_id, unsigned long a0,
>> + unsigned long a1, unsigned long a2)
>> +{
>> + ktime_t start, stop;
>> + int ret;
>> +
>> + if (!tpm_crb_ffa)
>> + return -ENOENT;
>> +
>> + start = ktime_get();
>> + stop = ktime_add(start, ms_to_ktime(busy_timeout_ms));
>> +
>> + for (;;) {
>> + ret = __tpm_crb_ffa_try_send_receive(func_id, a0, a1, a2);
>> +
>> + if (ret == -EBUSY) {
> This loop would be less convoluted if you instead:
>
> if (ret != -EBUSY)
> break;
>
> /* ... */
>
>> + usleep_range(50, 100);
> I wonder where this range comes from.
>
>> + if (ktime_after(ktime_get(), stop)) {
>> + dev_warn(&tpm_crb_ffa->ffa_dev->dev,
>> + "Busy retry timed out\n");
>> + break;
>> + }
>> + } else {
>> + break;
>> + }
>> + }
>>
>> return ret;
>> }
>> --
>> 2.43.0
>>
> BR, Jarkko
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