Re: [Qemu-devel] [PATCH v3 for-2.11 1/3] tpm_emulator: Add a caching layer for the TPM Established flag

[Marc-André Lureau]

Hi

On Tue, Nov 14, 2017 at 10:52 PM, Stefan Berger
<address@hidden> 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.

What's the impact? Isn't this just a "small" optimization? Iotw, why
is this for-2.11?

> Signed-off-by: Stefan Berger <address@hidden>
>
> v1->v2:
>  - move the caching to the backend layer since detecting the
>    TPM 1.2 TSC_ResetEstablishmentBit() command is easier to do
>    here.
> ---
>  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 e1a6810..b293db7 100644
> --- a/hw/tpm/tpm_emulator.c
> +++ b/hw/tpm/tpm_emulator.c
> @@ -73,6 +73,9 @@ typedef struct TPMEmulator {
>      Error *migration_blocker;
>
>      QemuMutex mutex;
> +
> +    unsigned int established_flag:1;
> +    unsigned int established_flag_cached:1;
>  } TPMEmulator;
>
>
> @@ -287,16 +290,22 @@ 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, 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,
> @@ -327,6 +336,8 @@ static int 
> tpm_emulator_reset_tpm_established_flag(TPMBackend *tb,
>          return -1;
>      }
>
> +    tpm_emu->established_flag_cached = 0;
> +
>      return 0;
>  }
>
> --
> 2.5.5
>



-- 
Marc-André Lureau