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

[Brijesh Singh]

On 10/26/2017 08:56 AM, Borislav Petkov wrote:
> On Mon, Oct 23, 2017 at 02:57:04PM -0500, Brijesh Singh wrote:
> > Calling PLATFORM_GET_STATUS is not required, we can manage the state through
> > a simple ref count variable. Issuing PSP commands will always be much more
> > expensive compare to accessing a protected global variable.
>
> What does "protected" mean here?

Access global variable after acquiring the semaphore.


> In any case, that variable can be a simple bool as you use it as such.

I am not using the variable (fw_init_count) as boolean. The variable 
gets incremented in sev_platform_init() and decremented in 
sev_platform_shutdown(). In very first call to sev_platform_init (i.e 
when variable is zero) we issue  PLATFORM_INIT command, similarly 
PLATFORM_SHUTDOWN is issued on the last (i.e when variable value is 
reached to zero). The variable is used as ref counter.


> > I would prefer to avoid invoking PSP command if possible.
> > Additionally, the global semaphore is still needed to serialize
> > the sev_platform_init() and sev_platform_shutdown() from multiple
> > processes. e.g If process "A" calls sev_platform_init() and if it gets
> > preempted due to whatever reason then we don't want another process
> > to issue the shutdown command while process "A" is in middle of
> > sev_platform_init().
>
> How? You're holding fw_init_mutex.

In your previous reply you comments on global semaphore (fw_init_mutex) 
and in response I tried to highlight why we need the global semaphore. 
Did I misunderstood your comment ?

-Brijesh