Date: Tue, 11 Aug 2026 07:48:34 -0700
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Message-ID: <ans2Qvo0453cc_DD@google.com>
Subject: Re: [PATCH v4 01/11] liveupdate: Add LIVEUPDATE_GUEST_MEMFD config option
From: Sean Christopherson <seanjc@google.com>
To: tarunsahu@google.com
Cc: ackerleytng@google.com, fuad.tabba@linux.dev, 
	Andrew Morton <akpm@linux-foundation.org>, dmatlack@google.com, 
	Shuah Khan <skhan@linuxfoundation.org>, Jonathan Corbet <corbet@lwn.net>, david@redhat.com, 
	Pasha Tatashin <pasha.tatashin@soleen.com>, Pratyush Yadav <pratyush@kernel.org>, sagis@google.com, 
	Paolo Bonzini <pbonzini@redhat.com>, Mike Rapoport <rppt@kernel.org>, Alexander Graf <graf@amazon.com>, 
	linux-kselftest@vger.kernel.org, andre.przywara@arm.com, michael.roth@amd.com, 
	linux-kernel@vger.kernel.org, linux-mm@kvack.org, will@kernel.org, 
	vannapurve@google.com, maz@kernel.org, fvdl@google.com, kvm@vger.kernel.org, 
	oliver.upton@linux.dev, kvmarm@lists.linux.dev, alexandru.elisei@arm.com, 
	skhawaja@google.com, aneesh.kumar@kernel.org, linux-doc@vger.kernel.org, 
	David Hildenbrand <david@kernel.org>, yan.y.zhao@intel.com, kexec@lists.infradead.org, 
	suzuki.poulose@arm.com
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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