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

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

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.
---
 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