[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Qemu-devel] [PATCH V13 2/7] Add TPM (frontend) hardware interface (

From: Stefan Berger
Subject: Re: [Qemu-devel] [PATCH V13 2/7] Add TPM (frontend) hardware interface (TPM TIS) to Qemu
Date: Mon, 12 Dec 2011 18:54:33 -0500
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20110928 Fedora/3.1.15-1.fc14 Lightning/1.0b3pre Thunderbird/3.1.15

On 12/12/2011 06:23 PM, Anthony Liguori wrote:
On 12/12/2011 01:12 PM, Stefan Berger wrote:
This patch adds the main code of the TPM frontend driver, the TPM TIS
interface, to Qemu. The code is largely based on the previous implementation
for Xen but has been significantly extended to meet the standard's
requirements, such as the support for changing of localities and all the
functionality of the available flags.

Communication with the backend (i.e., for Xen or the libtpms-based one)
is cleanly separated through an interface which the backend driver needs
to implement.

The TPM TIS driver's backend was previously chosen in the code added
to arch_init. The frontend holds a pointer to the chosen backend (interface).

Communication with the backend is largely based on signals and conditions.
Whenever the frontend has collected a complete packet, it will signal
the backend, which then starts processing the command. Once the result
has been returned, the backend invokes a callback function

The one tricky part is support for VM suspend while the TPM is processing
a command. In this case the frontend driver is waiting for the backend
to return the result of the last command before shutting down. It waits
on a condition for a signal from the backend, which is delivered in

Testing the proper functioning of the different flags and localities
cannot be done from user space when running in Linux for example, since
access to the address space of the TPM TIS interface is not possible. Also
the Linux driver itself does not exercise all functionality. So, for
testing there is a fairly extensive test suite as part of the SeaBIOS patches since from within the BIOS one can have full access to all the TPM's registers.

Signed-off-by: Stefan Berger<address@hidden>

+ * Send a TPM request.
+ * Call this with the state_lock held so we can sync with the receive
+ * callback.
+ */
+static void tpm_tis_tpm_send(TPMState *s, uint8_t locty)
+    TPMTISState *tis =&s->s.tis;
+#ifdef DEBUG_TIS
+    tpm_tis_show_buffer(&tis->loc[locty].w_buffer, "tpm_tis: To TPM");
+    s->command_locty = locty;
+    s->cmd_locty     =&tis->loc[locty];
+    /* w_offset serves as length indicator for length of data;
+       it's reset when the response comes back */
+    tis->loc[locty].state = TPM_TIS_STATE_EXECUTION;
+    tis->loc[locty].sts&= ~TPM_TIS_STS_EXPECT;
+    s->to_tpm_execute = true;
+    qemu_cond_signal(&s->to_tpm_cond);

The locking seems to presume that the device model is re-entrant which it's not today. Am I missing something here?

The TPM TIS frontend communicates with the TPM backend via a condition notifying it when a complete buffer with a TPM request has been received. The TPM backend is running as a thread, created via qemu_thread_create(). This is the design that was driven by the libtpms-based implementation.


reply via email to

[Prev in Thread] Current Thread [Next in Thread]