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

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

On 11/08/2017 03:37 PM, Stefan Berger 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>

Can anyone have a look, please?

      Stefan

>
> 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 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;
>   }
>