Re: [bug report] x86/sev: Split up runtime #VC handler for correct state tracking

[Dan Carpenter <dan.carpenter@oracle.com>]

On Wed, Aug 04, 2021 at 02:38:35PM +0200, Joerg Roedel wrote:
> Hi Dan,
> 
> On Wed, Aug 04, 2021 at 12:57:25PM +0300, Dan Carpenter wrote:
> > These sleeping in atomic static checker warnings come with a lot of
> > caveats because the call tree is very long and it's easy to have false
> > positives.
> > 
> > --> vc_raw_handle_exception()
> >     --> vc_forward_exception()
> >         --> exc_page_fault()
> > 
> > Page faults always sleep right?
> 
> No, page faults do no always sleep, only when IO needs to be done to
> fulfill the page fault request. In this case, the page-fault handler
> will never sleep, because it is called with preemption disabled. The
> page-fault handler can detect this and just do nothing. The #VC handler
> will return for re-fault in this case.

Hm...  Ok.  Let give you the rest of the call tree then because I'm not
seeing where it checks preempt count.

exc_page_fault() <-- called with preempt disabled
--> kvm_handle_async_pf()
    --> __kvm_handle_async_pf()
        --> kvm_async_pf_task_wait_schedule() calls schedule().

regards,
dan carpenter