Re: [Part2 PATCH v6 13/38] crypto: ccp: Add Secure Encrypted Virtualization (SEV) command support

[Brijesh Singh <brijesh.singh@amd.com>]

On 10/27/17 2:56 AM, Borislav Petkov wrote:
> On Thu, Oct 26, 2017 at 03:59:32PM -0500, Brijesh Singh wrote:
>> we can workaround #1 by adding some hooks in sp_pci_init() to invoke the PSP
>> initialization routines after pci_register_driver() is done but #2 can get
>> painful because it will require us calling the SHUTDOWN outside the
>> sp_pci_exit() code flow.
> Ok, do that and init the PSP master and then put the device in UNINIT
> state only in the functions which execute those commands which need the
> device to be in UNINIT state, e.g., wrap the SEV_CMD_FACTORY_RESET glue
> in a command function which does put the device in the UNINIT state as a
> first step.

transiting a platform in UINIT state to handle the FACTORY_RESET can
have a negative consequence.

Consider this scenario:

Process A
---------
sev_launch_start(...)

while (count < 10000) {
    sev_launch_update(...)
}

sev_launch_finish()
...
...

Process B:
---------
....
sev_factory_reset();
....

If in order to handle the FACTORY_RESET we  transition a platform in
UINIT state then it will results as unexpected failure from the
sev_launch_update() because the FACTORY_RESET command remove all the
state information created by sev_launch_start() etc. 

I think our design so far is simple, if command require INIT state then
caller executes sev_platform_init(), then command and finish with
sev_platform_shutdown(). If command does not require INIT state, then
simply issue the command. e.g currently, when caller issues
FACTORY_RESET then we pass command directly to PSP and if FW is in INIT
state then FACTORY_RESET returns error (INVALID_STATE/EBUSY) and we
propagate the error code to userspace.  User can retry the command
sometime later when nobody else is using the PSP.


>
> Then, when that function is done, put the device in the mode which the
> other commands would expect it to be in, e.g., INIT state.
>
> This way you'll simplify the whole command flow considerably and won't
> have to "toggle" the device each time and will save yourself a lot of
> time on command execution.
>
> Thx.
>