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 04:23:26PM +0200, Joerg Roedel wrote:
> On Wed, Aug 04, 2021 at 03:58:34PM +0300, Dan Carpenter wrote:
> > exc_page_fault() <-- called with preempt disabled
> > --> kvm_handle_async_pf()
> >     --> __kvm_handle_async_pf()
> >         --> kvm_async_pf_task_wait_schedule() calls schedule().
> 
> This call path can not be taken in the page-fault handler when called
> from the #VC handler. To take this path the host needs to inject an
> async page-fault, especially setting async pf flags, without injecting a
> page-fault exception on its own ... and when the #VC handler is running.
> KVM is not doing that.
> 
> Okay, the hypervisor can be malicious, but otherwise this can't happen.
> To mitigate a malicious hypervisor threat here it might be a solution to
> not call the page-fault handler directly from the #VC handler and let it
> re-fault after the #VC handler returned.
> 

Thanks for taking a look at this.

Also it turns out that my check wasn't taking in_atomic() into
consideration either so I've added that.

regards,
dan carpenter