From 93de2a6a4b91b72607136dd656edf03fb399d27f Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Wed, 23 Sep 2026 09:37:21 -0700 Subject: KVM: SEV: Do cache maintenance on the source VM during intra-host migration Manually perform cache maintenance on the source VM during intra-host migration to ensure no stale data is left in CPU caches after the VM is destroyed. Because the source VM is "converted" to a non-SEV VM, KVM's memory reclaim flows won't trigger cache maintenance, e.g. when all guest memory is reclaimed in response to detaching from the mmu_notifier. Note, relying on the destination VM to do cache maintenance isn't an option as KVM doesn't require identical guest memory configurations, i.e. the source VM may have access to memory that the destination VM does not. Enforcing equivalent memory configurations is infeasible, as it would require a *deep* comparison of memslots, e.g. to verify that not only are the memslot identical, but what the memslots point at is also identical. Fixes: b56639318bb2 ("KVM: SEV: Add support for SEV intra host migration") Cc: stable@vger.kernel.org Reported-by: Stefan Teodorescu Signed-off-by: Sean Christopherson Message-ID: <20260923163721.1584779-3-seanjc@google.com> Signed-off-by: Paolo Bonzini --- Documentation/admin-guide/sysctl/xen.rst | 31 +++++++++++++++++++++++++++++++ 1 file changed, 31 insertions(+) create mode 100644 Documentation/admin-guide/sysctl/xen.rst (limited to 'Documentation/admin-guide/sysctl/xen.rst') diff --git a/Documentation/admin-guide/sysctl/xen.rst b/Documentation/admin-guide/sysctl/xen.rst new file mode 100644 index 000000000..6c5edc3e5 --- /dev/null +++ b/Documentation/admin-guide/sysctl/xen.rst @@ -0,0 +1,31 @@ +=============== +/proc/sys/xen/ +=============== + +Copyright (c) 2026, Shubham Chakraborty + +For general info and legal blurb, please look in +Documentation/admin-guide/sysctl/index.rst. + +------------------------------------------------------------------------------ + +These files show up in ``/proc/sys/xen/``, depending on the +kernel configuration: + +.. contents:: :local: + +balloon/hotplug_unpopulated +=========================== + +This flag controls whether unpopulated memory ranges are automatically +hotplugged as system RAM. + +- ``0``: Unpopulated ranges are not hotplugged (default). +- ``1``: Unpopulated ranges are automatically hotplugged. + +When enabled, the Xen balloon driver will add memory regions that are +marked as unpopulated in the Xen memory map to the system as usable RAM. +This allows for dynamic memory expansion in Xen guest domains. + +This option is only available when the kernel is built with +``CONFIG_XEN_BALLOON_MEMORY_HOTPLUG`` enabled. -- cgit v1.3.1