Re: [PATCH v4 01/11] liveupdate: Add LIVEUPDATE_GUEST_MEMFD config option

[Sean Christopherson <seanjc@google.com>]

On Tue, Aug 11, 2026, tarunsahu@google.com wrote:
> Sean Christopherson <seanjc@google.com> writes:
> 
> > On Tue, Jul 28, 2026, Tarun Sahu wrote:
> >> Introduce the LIVEUPDATE_GUEST_MEMFD Kconfig option. This option
> >> enables live update support for KVM guest_memfd files, enabling
> >> guest_memfd-backed memory preservation across kernel upgrades.
> >> 
> >> Currently this support only guest_memfd files that are full-shared
> >> (INIT_SHARED and no support for private_mem).
> >
> > Why?  Specifically, why do we need/want a separate Kconfig for guest_memfd
> > liveupdate versus KVM liveupdate?  I can _maybe_ see a KVM-wide Kconfig, but
> > even that seems like a stretch given that (AFAIK) hypervisors are the one and
> > only use-case for liveupdate.
> 
> LIVEUPDATE is used in many subsystem. It is possible to enable
> liveupdate and kvm without enabling KVM_GUEST_MEMFD. So GUEST_MEMFD
> preservation must depend on CONFIG_LIVEUPDATE and KVM_GUEST_MEMFD both.
> LIVEUPDATE_GUEST_MEMFD Kconfig is wrapper on both of them. It need not
> to be visible in menu, So I can make it hidden. WDYT?
> 
> Also, KVM VM_FILE preservation and GUEST_MEMFD preservation both depends
> on LIVEUPDATE_GUEST_MEMFD in this patch series. [PATCH 05/11]*
> Which is wrong. So I will update KVM VM_FILE preservation to depend only
> on CONFIG_LIVEUPDATE.

Or just handle it all in the makefile?  E.g.

diff --git virt/kvm/Makefile.kvm virt/kvm/Makefile.kvm
index d047d4cf58c9..e6f098498795 100644
--- virt/kvm/Makefile.kvm
+++ virt/kvm/Makefile.kvm
@@ -13,3 +13,8 @@ kvm-$(CONFIG_HAVE_KVM_IRQ_ROUTING) += $(KVM)/irqchip.o
 kvm-$(CONFIG_HAVE_KVM_DIRTY_RING) += $(KVM)/dirty_ring.o
 kvm-$(CONFIG_HAVE_KVM_PFNCACHE) += $(KVM)/pfncache.o
 kvm-$(CONFIG_KVM_GUEST_MEMFD) += $(KVM)/guest_memfd.o
+
+ifdef CONFIG_LIVEUPDATE
+kvm-y += $(KVM)/kvm_luo.o
+kvm-$(CONFIG_KVM_GUEST_MEMFD) += $(KVM)/guest_memfd_luo.o
+endif