Re: [PATCH v7 4/6] tpm_spapr: Support suspend and resume

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

On 1/2/20 7:19 PM, David Gibson wrote:
> On Thu, Dec 19, 2019 at 09:06:03AM -0500, Stefan Berger wrote:
>> Extend the tpm_spapr frontend with VM suspend and resume support.
>>
>> Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
>> ---
>>   hw/tpm/tpm_spapr.c  | 67 ++++++++++++++++++++++++++++++++++++++++++++-
>>   hw/tpm/trace-events |  2 ++
>>   2 files changed, 68 insertions(+), 1 deletion(-)
>>
>> diff --git a/hw/tpm/tpm_spapr.c b/hw/tpm/tpm_spapr.c
>> index ab184fbb82..cf5c7851e7 100644
>> --- a/hw/tpm/tpm_spapr.c
>> +++ b/hw/tpm/tpm_spapr.c
>> @@ -76,6 +76,9 @@ typedef struct {
>>   
>>       unsigned char buffer[TPM_SPAPR_BUFFER_MAX];
>>   
>> +    uint32_t numbytes; /* number of bytes in suspend_buffer */
>> +    unsigned char *suspend_buffer;
>> +
>>       TPMBackendCmd cmd;
>>   
>>       TPMBackend *be_driver;
>> @@ -240,6 +243,13 @@ static void tpm_spapr_request_completed(TPMIf *ti, int ret)
>>   
>>       /* a max. of be_buffer_size bytes can be transported */
>>       len = MIN(tpm_cmd_get_size(s->buffer), s->be_buffer_size);
>> +
>> +    if (runstate_check(RUN_STATE_FINISH_MIGRATE)) {
>> +        /* defer delivery of response until .post_load */
>> +        s->numbytes = len;
>> +        return;
>> +    }
> I'm not understanding the basics of what's going on here.  IIUC, the
> backend TPM can complete a request after we've entered migration


The tpm_backend_finish_sync() in the .pre_save function will delay the 
writing of the device state until all outstanding responses have been 
captured. In case a response was outstanding, the above s->numbytes will 
then be set and looked at after return from tpm_backend_finish_sync() -- 
see below.


> downtime.  But if that's the case, I can't see any guarantee that we
> won't have already transmitted the TPM device state, so updating it
> here might never reach the destination.  In that case we'd still lose
> the request, so I'm not sure what we're accomplishing here.
>
>>       rc = spapr_vio_dma_write(&s->vdev, be32_to_cpu(crq->data),
>>                                s->buffer, len);
>>   
>> @@ -288,11 +298,13 @@ static void tpm_spapr_reset(SpaprVioDevice *dev)
>>       SpaprTpmState *s = VIO_SPAPR_VTPM(dev);
>>   
>>       s->state = SPAPR_VTPM_STATE_NONE;
>> +    s->numbytes = 0;
>>   
>>       s->be_tpm_version = tpm_backend_get_tpm_version(s->be_driver);
>>   
>>       s->be_buffer_size = MIN(tpm_backend_get_buffer_size(s->be_driver),
>>                               TPM_SPAPR_BUFFER_MAX);
>> +    s->suspend_buffer = g_realloc(s->suspend_buffer, s->be_buffer_size);
>>   
>>       tpm_backend_reset(s->be_driver);
>>       tpm_spapr_do_startup_tpm(s, s->be_buffer_size);
>> @@ -309,9 +321,62 @@ static enum TPMVersion tpm_spapr_get_version(TPMIf *ti)
>>       return tpm_backend_get_tpm_version(s->be_driver);
>>   }
>>   
>> +/* persistent state handling */
>> +
>> +static int tpm_spapr_pre_save(void *opaque)
>> +{
>> +    SpaprTpmState *s = opaque;
>> +
>> +    tpm_backend_finish_sync(s->be_driver);
>> +
>> +    if (s->numbytes) {
>> +        memcpy(s->suspend_buffer, s->buffer, s->numbytes);
>> +    }
>> +
>> +    trace_tpm_spapr_pre_save(s->numbytes);
>> +    /*
>> +     * we cannot deliver the results to the VM since DMA would touch VM memory
>> +     */
>> +
>> +    return 0;
>> +}
>> +
>> +static int tpm_spapr_post_load(void *opaque, int version_id)
>> +{
>> +    SpaprTpmState *s = opaque;
>> +
>> +    if (s->numbytes) {
>> +        trace_tpm_spapr_post_load();
>> +
>> +        memcpy(s->buffer, s->suspend_buffer,
>> +               MIN(s->numbytes, s->be_buffer_size));
>> +        /* deliver the results to the VM via DMA */
>> +        tpm_spapr_request_completed(TPM_IF(s), 0);
>> +        s->numbytes = 0;
>> +    }
>> +
>> +    return 0;
>> +}
>> +
>>   static const VMStateDescription vmstate_spapr_vtpm = {
>>       .name = "tpm-spapr",
>> -    .unmigratable = 1,
>> +    .version_id = 1,
>> +    .minimum_version_id = 0,
>> +    .minimum_version_id_old = 0,
>> +    .pre_save = tpm_spapr_pre_save,
>> +    .post_load = tpm_spapr_post_load,
>> +    .fields = (VMStateField[]) {
>> +        VMSTATE_SPAPR_VIO(vdev, SpaprTpmState),
>> +
>> +        VMSTATE_UINT8(state, SpaprTpmState),
>> +        VMSTATE_UINT32(numbytes, SpaprTpmState),
>> +        VMSTATE_VBUFFER_ALLOC_UINT32(suspend_buffer,
>> +                                     SpaprTpmState, 0, NULL,
>> +                                     numbytes),
>> +        /* remember DMA address */
>> +        VMSTATE_UINT32(crq.data, SpaprTpmState),
>> +        VMSTATE_END_OF_LIST(),
>> +    }
>>   };
>>   
>>   static Property tpm_spapr_properties[] = {
>> diff --git a/hw/tpm/trace-events b/hw/tpm/trace-events
>> index 9143a8eaa3..5592cec7de 100644
>> --- a/hw/tpm/trace-events
>> +++ b/hw/tpm/trace-events
>> @@ -67,3 +67,5 @@ tpm_spapr_do_crq_get_version(uint32_t version) "response: version %u"
>>   tpm_spapr_do_crq_prepare_to_suspend(void) "response: preparing to suspend"
>>   tpm_spapr_do_crq_unknown_msg_type(uint8_t type) "Unknown message type 0x%02x"
>>   tpm_spapr_do_crq_unknown_crq(uint8_t raw1, uint8_t raw2) "unknown CRQ 0x%02x 0x%02x ..."
>> +tpm_spapr_pre_save(uint32_t v) "Number of TPM response bytes to deliver after resume: %u"
>> +tpm_spapr_post_load(void) "Delivering TPM response after resume"