Re: [Qemu-devel] [PATCH v2] tpm_emulator: Add a caching layer for the TPM Established flag

[Stefan Berger <stefanb@linux.vnet.ibm.com>]

On 11/09/2017 07:07 AM, Marc-André Lureau wrote:
> Hi
>
> On Wed, Nov 8, 2017 at 9:37 PM, Stefan Berger
> <stefanb@linux.vnet.ibm.com> wrote:
>> Add a caching layer for the TPM established flag so that we don't
>> need to go to the emulator every time the flag is read by accessing
>> the REG_ACCESS register.
>>
>> Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
>>
>> v1->v2:
>>   - move the caching to the backend layer since detecting the
>>     TPM 1.2 TSC_ResetEstablishmentBit() command is easier to do
>>     here.
> What about the HASH_START? Is this not supported by qemu TIS? Is the
> function gone or done differently with TPM2 or CRB?

Afaik, HASH_START would need emulation of CPU instructions to initiate 
it. Reading this flag from the device is there primarily for 
completeness reasons.

     Stefan

>
>> ---
>>   hw/tpm/tpm_emulator.c | 17 ++++++++++++++---
>>   1 file changed, 14 insertions(+), 3 deletions(-)
>>
>> diff --git a/hw/tpm/tpm_emulator.c b/hw/tpm/tpm_emulator.c
>> index 9aaec8e..507e2cb 100644
>> --- a/hw/tpm/tpm_emulator.c
>> +++ b/hw/tpm/tpm_emulator.c
>> @@ -71,6 +71,9 @@ typedef struct TPMEmulator {
>>       ptm_cap caps; /* capabilities of the TPM */
>>       uint8_t cur_locty_number; /* last set locality */
>>       Error *migration_blocker;
>> +
>> +    unsigned int established_flag:1;
>> +    unsigned int established_flag_cached:1;
>>   } TPMEmulator;
>>
>>
>> @@ -277,16 +280,22 @@ static bool tpm_emulator_get_tpm_established_flag(TPMBackend *tb)
>>       TPMEmulator *tpm_emu = TPM_EMULATOR(tb);
>>       ptm_est est;
>>
>> -    DPRINTF("%s", __func__);
>> +    if (tpm_emu->established_flag_cached) {
>> +        return tpm_emu->established_flag;
>> +    }
>> +
>>       if (tpm_emulator_ctrlcmd(&tpm_emu->ctrl_chr, CMD_GET_TPMESTABLISHED, &est,
>>                                0, sizeof(est)) < 0) {
>>           error_report("tpm-emulator: Could not get the TPM established flag: %s",
>>                        strerror(errno));
>>           return false;
>>       }
>> -    DPRINTF("established flag: %0x", est.u.resp.bit);
>> +    DPRINTF("got established flag: %0x", est.u.resp.bit);
>> +
>> +    tpm_emu->established_flag_cached = 1;
>> +    tpm_emu->established_flag = (est.u.resp.bit != 0);
>>
>> -    return (est.u.resp.bit != 0);
>> +    return tpm_emu->established_flag;
>>   }
>>
>>   static int tpm_emulator_reset_tpm_established_flag(TPMBackend *tb,
>> @@ -317,6 +326,8 @@ static int tpm_emulator_reset_tpm_established_flag(TPMBackend *tb,
>>           return -1;
>>       }
>>
>> +    tpm_emu->established_flag_cached = 0;
>> +
>>       return 0;
>>   }
>>
>> --
>> 2.5.5
>>
>>
>
>