KVM: x86: Don't check for code breakpoints when emulating on exception

KVM: x86: Don't check for code breakpoints when emulating on exception

Don't check for code breakpoints during instruction emulation if the
emulation was triggered by exception interception.  Code breakpoints are
the highest priority fault-like exception, and KVM only emulates on
exceptions that are fault-like.  Thus, if hardware signaled a different
exception, then the vCPU is already passed the stage of checking for
hardware breakpoints.

This is likely a glorified nop in terms of functionality, and is more for
clarification and is technically an optimization.  Intel's SDM explicitly
states vmcs.GUEST_RFLAGS.RF on exception interception is the same as the
value that would have been saved on the stack had the exception not been
intercepted, i.e. will be '1' due to all fault-like exceptions setting RF
to '1'.  AMD says "guest state saved ... is the processor state as of the
moment the intercept triggers", but that begs the question, "when does
the intercept trigger?".

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Link: https://lore.kernel.org/r/20220830231614.3580124-4-seanjc@google.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>