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Date:   Wed, 11 May 2022 14:16:23 +0000
From:   Sean Christopherson <seanjc@google.com>
To:     Arnabjyoti Kalita <akalita@cs.stonybrook.edu>
Cc:     Jim Mattson <jmattson@google.com>, kvm@vger.kernel.org
Subject: Re: Causing VMEXITs when kprobes are hit in the guest VM
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On Wed, May 11, 2022, Arnabjyoti Kalita wrote:
> Hello Jim and Sean,
> 
> Thank you for your answers.
> 
> If I re-inject the #BP back into the guest, does it automatically take
> care of updating the RIP and continuing execution?

Yes, the guest "automatically" handles the #BP.  What the appropriate handling may
be is up to the guest, i.e. skipping an instruction may or may not be the correct
thing to do.  Injecting the #BP after VM-Exit is simply emulating what would happen
from the guest's perspective if KVM had never intercepted the #BP in the first place.

Note, KVM doesn't have to initiate the injection, you can handle that from userspace
via KVM_SET_VCPU_EVENTS.  But if it's just as easy to hack KVM, that's totally fine
too, so long as userspace doesn't double inject.