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


From: Stefan Berger
Subject: Re: [Qemu-devel] [PATCH v2] tpm_emulator: Add a caching layer for the TPM Established flag
Date: Mon, 13 Nov 2017 12:13:13 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0

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 <address@hidden>

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;
  }





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