Re: [PATCH] mmc: rpmb: do not force a retune before RPMB switch

Adrian Hunter
2023-12-11T11:33:15Z

On 11/12/23 13:06, Jorge Ramirez-Ortiz, Foundries wrote:
> On 11/12/23 12:25:19, Adrian Hunter wrote:
>> On 11/12/23 10:00, Jorge Ramirez-Ortiz, Foundries wrote:
>>> On 06/12/23 11:00:47, Jorge Ramirez-Ortiz, Foundries wrote:
>>>> On 06/12/23 07:02:43, Avri Altman wrote:
>>>>>>
>>>>>> On 4/12/23 17:01, Jorge Ramirez-Ortiz wrote:
>>>>>>> Requesting a retune before switching to the RPMB partition has been
>>>>>>> observed to cause CRC errors on the RPMB reads (-EILSEQ).
>>>>>>
>>>>>> There are still 2 concerns:
>>>>>> 1) We don't really know the root cause. Have you determined if here are
>>>>>> CRC errors in the main partition also?
>>>>
>>>> right, and I don't disagree with that.
>>>>
>>>> As a test I created a 4GB file from /dev/random which I then copied
>>>> several times (dd if= ....)
>>>>
>>>> root@uz3cg-dwg-sec:/sys/kernel/debug/mmc0# cat err_stats
>>>> # Command Timeout Occurred: 0
>>>> # Command CRC Errors Occurred: 0
>>>> # Data Timeout Occurred: 0
>>>> # Data CRC Errors Occurred: 0
>>>> # Auto-Cmd Error Occurred: 0
>>>> # ADMA Error Occurred: 0
>>>> # Tuning Error Occurred: 0
>>>> # CMDQ RED Errors: 0
>>>> # CMDQ GCE Errors: 0
>>>> # CMDQ ICCE Errors: 0
>>>> # Request Timedout: 0
>>>> # CMDQ Request Timedout: 0
>>>> # ICE Config Errors: 0
>>>> # Controller Timedout errors: 0
>>>> # Unexpected IRQ errors: 0
>>>>
>>>> However as soon as I access RPMB and fails (it takes just a few tries) I see:
>>>>
>>>> I/TC: RPMB: Using generated key
>>>> [ 86.902118] sdhci-arasan ff160000.mmc: __mmc_blk_ioctl_cmd: data error -84
>>>> E/TC:? 0
>>>> E/TC:? 0 TA panicked with code 0xffff0000
>>>> E/LD: Status of TA 22250a54-0bf1-48fe-8002-7b20f1c9c9b1
>>>> E/LD: arch: aarch64
>>>> E/LD: region 0: va 0xc0004000 pa 0x7e200000 size 0x002000 flags rw-s (ldelf)
>>>> E/LD: region 1: va 0xc0006000 pa 0x7e202000 size 0x008000 flags r-xs (ldelf)
>>>> E/LD: region 2: va 0xc000e000 pa 0x7e20a000 size 0x001000 flags rw-s (ldelf)
>>>> E/LD: region 3: va 0xc000f000 pa 0x7e20b000 size 0x004000 flags rw-s (ldelf)
>>>> E/LD: region 4: va 0xc0013000 pa 0x7e20f000 size 0x001000 flags r--s
>>>> E/LD: region 5: va 0xc0014000 pa 0x7e22c000 size 0x005000 flags rw-s (stack)
>>>> E/LD: region 6: va 0xc0019000 pa 0x818ea9ba8 size 0x002000 flags rw-- (param)
>>>> E/LD: region 7: va 0xc001b000 pa 0x818e97ba8 size 0x001000 flags rw-- (param)
>>>> E/LD: region 8: va 0xc004f000 pa 0x00001000 size 0x014000 flags r-xs [0]
>>>> E/LD: region 9: va 0xc0063000 pa 0x00015000 size 0x008000 flags rw-s [0]
>>>> E/LD: [0] 22250a54-0bf1-48fe-8002-7b20f1c9c9b1 @ 0xc004f000
>>>> E/LD: Call stack:
>>>> E/LD: 0xc0051a14
>>>> E/LD: 0xc004f31c
>>>> E/LD: 0xc0052d40
>>>> E/LD: 0xc004f624
>>>>
>>>> root@uz3cg-dwg-sec:/var/rootdirs/home/fio# cat /sys/kernel/debug/mmc0/err_stats
>>>> # Command Timeout Occurred: 0
>>>> # Command CRC Errors Occurred: 0
>>>> # Data Timeout Occurred: 0
>>>> # Data CRC Errors Occurred: 1
>>>> # Auto-Cmd Error Occurred: 0
>>>> # ADMA Error Occurred: 0
>>>> # Tuning Error Occurred: 0
>>>> # CMDQ RED Errors: 0
>>>> # CMDQ GCE Errors: 0
>>>> # CMDQ ICCE Errors: 0
>>>> # Request Timedout: 0
>>>> # CMDQ Request Timedout: 0
>>>> # ICE Config Errors: 0
>>>> # Controller Timedout errors: 0
>>>> # Unexpected IRQ errors: 0
>>>>
>>>>>> 2) Forcing this on everyone
>>>>>>
>>>>>> The original idea was that because re-tuning cannot be done in RPMB, the
>>>>>> need to re-rune in RPMB could be avoided by always re-tuning before
>>>>>> switching to RPMB and then switching straight back. IIRC re-tuning should
>>>>>> guarantee at least 4MB more I/O without issue.
>>>>> Performance is hardly an issue in the context of RPMB access -
>>>>> For most cases it’s a single frame.
>>>>
>>>> Yes, the security use case typically stores hashes, variables
>>>> (bootcount, upgrade_available, versions, that sort of thing) and
>>>> certificates in RPMB.
>>>>
>>>> Since you mentioned, I am seeing that tuning before switching to RPMB
>>>> has an impact on performance. As a practical test, just reading a 6 byte
>>>> variable incurs in 50ms penalty in kernel space due to the need to
>>>> retune 5 times. Not great since the request is coming from a Trusted
>>>> Application via OP-TEE through the supplicant meaning this TEE thread
>>>> (they are statically allocated CFG_NUM_THREADS) will be reserved for
>>>> quite a bit of time.
>>>>
>>>> Roughly:
>>>> TA --> OP-TEE (core) --> TEE-supplicant --> Kernel (>50ms) --> OP-TEE --> TA
>>>
>>> To add more detail to the timing above, when using RPMB, OP-TEE stores
>>> the secure filesystem on RPMB as well, so accessing one of the variables
>>> stored in the filesystem consists on a number (~5) of individual RPMB
>>> requests (each one forcing a retune, each retune taking around 10ms).
>>>
>>> BTW, I also tried delaying the timing between those consecutive retunes
>>> (up to 1 second), but the issue still persisted.
>>>
>>>>
>>>> Adrian, I couldn't find the original performance justification for
>>>> enabling this feature globally. At which point do you think it becomes
>>>> beneficial to retune before accessing RPMB?
>>>
>>> How should we proceed with this patch then? can it be merged as I
>>> proposed? should I rewrite it differently? not sure what is next
>>
>> It would be good to try to determine if the error happens when the
>> switch command comes immediately after tuning. For example, add
>> a delay after tuning and see if that makes any difference. e.g.
>>
>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
>> index c79f73459915..6b168659282a 100644
>> --- a/drivers/mmc/host/sdhci.c
>> +++ b/drivers/mmc/host/sdhci.c
>> @@ -2867,8 +2867,10 @@ int __sdhci_execute_tuning(struct sdhci_host *host, u32 opcode)
>>
>> ctrl = sdhci_readw(host, SDHCI_HOST_CONTROL2);
>> if (!(ctrl & SDHCI_CTRL_EXEC_TUNING)) {
>> - if (ctrl & SDHCI_CTRL_TUNED_CLK)
>> + if (ctrl & SDHCI_CTRL_TUNED_CLK) {
>> + msleep(10);
>> return 0; /* Success! */
>> + }
>> break;
>> }
>>
>>
>
> Thanks Adrian.
>
> The issue sill triggers (in this case on the last but one access to
> retrieve the 6 byte variable).
>
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -2781,6 +2781,7 @@ static int __sdhci_execute_tuning(struct sdhci_host *host, u32 opcode)
> * Issue opcode repeatedly till Execute Tuning is set to 0 or the number
> * of loops reaches tuning loop count.
> */
> + printk(KERN_ERR "tune starts[loop %d]\n", host->tuning_loop_count);
> for (i = 0; i < host->tuning_loop_count; i++) {
> u16 ctrl;
>
> @@ -2799,8 +2800,11 @@ static int __sdhci_execute_tuning(struct sdhci_host *host, u32 opcode)
>
> ctrl = sdhci_readw(host, SDHCI_HOST_CONTROL2);
> if (!(ctrl & SDHCI_CTRL_EXEC_TUNING)) {
> - if (ctrl & SDHCI_CTRL_TUNED_CLK)
> - return 0; /* Success! */
> + if (ctrl & SDHCI_CTRL_TUNED_CLK) {
> + printk(KERN_ERR "tune success[%d]\n", i);
> + msleep(10);
> + return 0; /* Success! */
> + }
> break;
> }
>
>
> [ 164.919090] tune starts[loop 40]
> [ 164.923152] tune success[39]
> [ 164.952106] tune starts[loop 40]
> [ 164.956611] tune success[39]
> [ 165.084402] tune starts[loop 40]
> [ 165.089350] tune success[39]
> [ 165.116491] tune starts[loop 40]
> [ 165.120806] tune success[39]
> [ 165.145016] sdhci-arasan ff160000.mmc: __mmc_blk_ioctl_cmd: data error -84
> E/TC:? 0
> E/TC:? 0 TA panicked with code 0xffff0000
> E/LD: Status of TA 22250a54-0bf1-48fe-8002-7b20f1c9c9b1
> E/LD: arch: aarch64
> E/LD: region 0: va 0xc0004000 pa 0x7e200000 size 0x002000 flags rw-s (ldelf)
> E/LD: region 1: va 0xc0006000 pa 0x7e202000 size 0x008000 flags r-xs (ldelf)
> E/LD: region 2: va 0xc000e000 pa 0x7e20a000 size 0x001000 flags rw-s (ldelf)
> E/LD: region 3: va 0xc000f000 pa 0x7e20b000 size 0x004000 flags rw-s (ldelf)
> E/LD: region 4: va 0xc0013000 pa 0x7e20f000 size 0x001000 flags r--s
> E/LD: region 5: va 0xc0014000 pa 0x7e22c000 size 0x005000 flags rw-s (stack)
> E/LD: region 6: va 0xc0019000 pa 0x818ac38e8 size 0x001000 flags rw-- (param)
> E/LD: region 7: va 0xc001a000 pa 0x818ac36e8 size 0x001000 flags rw-- (param)
> E/LD: region 8: va 0xc0022000 pa 0x00001000 size 0x014000 flags r-xs [0]
> E/LD: region 9: va 0xc0036000 pa 0x00015000 size 0x008000 flags rw-s [0]
> E/LD: [0] 22250a54-0bf1-48fe-8002-7b20f1c9c9b1 @ 0xc0022000
> E/LD: Call stack:
> E/LD: 0xc0024e58
> E/LD: 0xc0022388
> E/LD: 0xc0025d40
> E/LD: 0xc0022624
> [ 166.119598] tune starts[loop 40]
> [ 166.125700] tune success[39]

It might make a difference if there is another command before the
switch command, e.g. add a CMD13 (could keep the tune print to tell
that the CMD13 comes after re-tuning)

diff --git a/drivers/mmc/core/block.c b/drivers/mmc/core/block.c
index 892e74e611a0..3265049f4132 100644
--- a/drivers/mmc/core/block.c
+++ b/drivers/mmc/core/block.c
@@ -875,6 +875,7 @@ static int mmc_blk_part_switch_pre(struct mmc_card *card,
unsigned int part_type)
{
int ret = 0;
+ u32 status;

if (part_type == EXT_CSD_PART_CONFIG_ACC_RPMB) {
if (card->ext_csd.cmdq_en) {
@@ -883,6 +884,9 @@ static int mmc_blk_part_switch_pre(struct mmc_card *card,
return ret;
}
mmc_retune_pause(card->host);
+ ret = mmc_send_status(card, &status);
+ pr_info("%s: %s: status %#x, ret %d\n", mmc_hostname(card->host), __func__, status, ret);
+ ret = 0;
}

return ret;

And another thing to try is SDHCI_QUIRK2_TUNING_WORK_AROUND