On 11/14/2017 06:40 PM, Marc-André Lureau wrote:
Hi
On Tue, Nov 14, 2017 at 10:52 PM, Stefan Berger
<stef...@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.
What's the impact? Isn't this just a "small" optimization? Iotw, why
is this for-2.11?
The TIS has a register that contains this flag and that's being polled
quite frequently. So it generates a lot of traffic to the emulator. This
caching layer gets rid of most of the traffic.
Stefan
Signed-off-by: Stefan Berger <stef...@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 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