KVM: VMX: Move preemption timer <=> hrtimer dance to common x86

commit 98c25ead upstream.

Handle the switch to/from the hypervisor/software timer when a vCPU is
blocking in common x86 instead of in VMX.  Even though VMX is the only
user of a hypervisor timer, the logic and all functions involved are
generic x86 (unless future CPUs do something completely different and
implement a hypervisor timer that runs regardless of mode).

Handling the switch in common x86 will allow for the elimination of the
pre/post_blocks hooks, and also lets KVM switch back to the hypervisor
timer if and only if it was in use (without additional params).  Add a
comment explaining why the switch cannot be deferred to kvm_sched_out()
or kvm_vcpu_block().

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20211208015236.1616697-8-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[ta: Fix conflicts in vmx_pre_block and vmx_post_block as per Paolo's
suggestion. Add Reported-by and Link tags.]
Reported-by:  <syzbot+b6a74be92b5063a0f1ff@syzkaller.appspotmail.com>
Link: https://syzkaller.appspot.com/bug?id=489beb3d76ef14cc6cd18125782dc6f86051a605


Tested-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>