Re: [Qemu-devel] vNVRAM / blobstore design

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Mar 27, 2013 at 11:20:43AM -0400, Corey Bryant wrote:
> 
> 
> On 03/27/2013 11:17 AM, Corey Bryant wrote:
> >
> >
> >On 03/25/2013 06:20 PM, Stefan Berger wrote:
> >>On 03/25/2013 06:05 PM, Anthony Liguori wrote:
> >>>Stefan Berger <stefanb@linux.vnet.ibm.com> writes:
> >>>
> >>>>[argh, just posted this to qemu-trivial -- it's not trivial]
> >>>>
> >>>>
> >>>>Hello!
> >>>>
> >>>>I am posting this message to revive the previous discussions about the
> >>>>design of vNVRAM / blobstore cc'ing (at least) those that participated
> >>>>in this discussion 'back then'.
> >>>>
> >>>>The first goal of the implementation is to provide an vNVRAM storage
> >>>>for
> >>>>a software implementation of a TPM to store its different blobs into.
> >>>>Some of the data that the TPM writes into persistent memory needs to
> >>>>survive a power down / power up cycle of a virtual machine, therefore
> >>>>this type of persistent storage is needed. For the vNVRAM not to become
> >>>>a road-block for VM migration, we would make use of block device
> >>>>migration and layer the vNVRAM on top of the block device, therefore
> >>>>using virtual machine images for storing the vNVRAM data.
> >>>>
> >>>>Besides the TPM blobs the vNVRAM should of course also be able able to
> >>>>accommodate other use cases where persistent data is stored into
> >>>>NVRAM,
> >>>Well let's focus more on the "blob store".  What are the semantics of
> >>>this?  Is there a max number of blobs?  Are the sizes fixed or variable?
> >>>How often are new blobs added/removed?
> >
> >The max number of blobs and frequency of usage depends on the usage
> >scenario and NVRAM size.  But that's probably obvious.
> >
> >I think we should focus on worst case scenarios where NVRAM is filled up
> >and used frequently.
> >
> >One example is that an application can use TSS APIs to define, undefine,
> >read, and write to the TPM's NVRAM storage.  (The TPM owner password is
> >required to define NVRAM data.)  An application could potentially fill
> >up NVRAM and frequently store, change, retrieve data in various places
> >within NVRAM.  And the data could have various sizes.
> >
> >For an example of total NVRAM size, Infineon's TPM has 16K of NVRAM.
> >
> >--
> >Regards,
> >Corey Bryant
> >
> 
> I just wanted to add that we could really use some direction on
> which way the community would prefer we go with this.  The 2 options
> that are on the table at the moment for encoding/decoding the vNVRAM
> byte stream are BER or JSON visitors.
> 
> -- 
> Regards,
> Corey Bryant

I think I like BER better. JSON seems like a bad fit for a
bunch of binary blobs.

> >>
> >>In case of TPM 1.2 there are 3 blobs that can be written at different
> >>times for different reasons.
> >>
> >>Examples: As with a real-world TPM users loading an owner-evict key into
> >>the TPM will cause the TPM to write that owner-evict key into is own
> >>NVRAM. This key survives a power-off of the machine. Further, the TPM
> >>models its own NVRAM slots. Someone writing into this type of memory
> >>will cause data to be written into the NVRAM. There are other commands
> >>that the TPM offers that will cause data to be written into NVRAM which
> >>users can invoke at any time.
> >>
> >>The sizes of the NVRAM blobs of the TPM at least vary in size but I
> >>handle this in the TPM emulation to pad them to fixed size. Depending on
> >>how many such owner-evict keys are loaded into the TPM its permanent
> >>state blob size may vary. Other devices may act differently.
> >>
> >>We have a-priori knowledge about  the 3 different types of blobs the TPM
> >>device produces. They are 'registered' once at the beginning (see API)
> >>and are not 'removed' as such.
> >>
> >>Regards,
> >>     Stefan
> >>
> >