On 8/21/26 14:34, Garg, Shivank wrote: > On Wed, 2026-08-05 at 06:40 +0000, Shivank Garg wrote: >> guest_memfd folios are currently always marked unmovable, so the kernel >> cannot >> perform memory compaction, offlining, etc. This is unavoidable for >> confidential VMs (SEV-SNP, TDX), since memory is encrypted and copying it >> needs firmware assistance. However, for non-confidential VMs (like >> Firecracker), we can migrate the folios. >> >> This series enables folio migration for non-confidential guest_memfd and >> also lays the groundwork for migrating confidential guest_memfd later. >> Once firmware-assisted copying support is available, those VMs can be >> made movable, the confidential folio content can be copied separately, >> and the destination folio marked with FOLIO_CONTENT_COPIED[4] so >> __migrate_folio() skips the host-side folio_mc_copy(). >> >> Testing >> ------- >> Host: 7.2-rc6+(c21bb419386) + this, AMD EPYC ZEN 3, 2 NUMA nodes >> >> - KVM selftest: allocate folios on node 0, migrate them to node 1 and >> back and verify resulting NUMA node and the folio contents at each >> step. >> >> - Firecracker [1]: booted a microVM backed by guest_memfd. While the >> guest was running, forced host-side migration of its folios via >> migratepages(8) and explicit move_pages(2) of guest_memfd >> pages. Verify with /proc/firecracker_pid/numa_maps. >> >> Notes >> ----- >> - Sashiko pointed out a pre-existing ABBA deadlock between >> kvm_gmem_error_folio() and truncation. It's being addressed separately >> by Hao Zhang. [2][3] >> >> [1] >> https://github.com/firecracker-microvm/firecracker/tree/feature/secret-hiding >> In builder.rs, add GUEST_MEMFD_FLAG_MIGRATABLE to bit-2 and pass it >> instead >> of GUEST_MEMFD_FLAG_NO_DIRECT_MAP to vm.create_guest_memfd(). >> [2] https://lore.kernel.org/all/[email protected]/ >> [3] >> https://sashiko.dev/#/patchset/20260611-shivank-gmem-migrate-v1-0-2d266bfc6f95%40amd.com >> [4] >> https://lore.kernel.org/all/[email protected] >> >> Signed-off-by: Shivank Garg <[email protected]> >> --- >> Changes in v3: >> - Fix unbalanced mmu_invalidate_in_progress count unbinding dying >> guest_memfd. (Sashiko) >> - Fix maxnode handling in xapic_ipi_test selftest. >> - Add GUEST_MEMFD_FLAG_MIGRATABLE documentation >> - Replace open-coded sizeof() * 8 calculation with BITS_PER_TYPE() >> - Add get_numa_mem_nodes() and use MPOL_F_MEMS_ALLOWED for allowed NUMA >> ndoes >> instead of hardcoded NUMA node IDs. (Sashiko) >> - Extend migration selftest to verify rejection without MIGRATABLE flag and >> move repeated checks into common helpers. >> - Drop RFC tag. >> - Link to v2: >> https://lore.kernel.org/r/[email protected] >> >> Changes in v2: >> - Make folio migration opt-in through GUEST_MEMFD_FLAG_MIGRATABLE, >> preserving unmovable behavior if userspace don't explictly ask. >> (Alexandru, David, Sean) >> - Add kvm_arch_supports_gmem_migration() so arch can control whether >> GUEST_MEMFD_FLAG_MIGRATABLE is advertised. >> - Allocate movable folios with GFP_HIGHUSER_MOVABLE. (David) >> - Keep guest_memfd unevictable. (David, Sashiko, Sean) >> - Split migrate_folio() implementation and enablement as separate patches. >> - Update selftest with new flag. >> - Link to v1: >> https://lore.kernel.org/r/[email protected] >> >> --- >> Shivank Garg (9): >> KVM: guest_memfd: take the invalidate lock when unbinding a dying file >> mm: split AS_UNMOVABLE back out of AS_INACCESSIBLE >> KVM: guest_memfd: implement folio migration for non-confidential VMs >> KVM: guest_memfd: add GUEST_MEMFD_FLAG_MIGRATABLE >> KVM: selftests: fix maxnode arguments in xapic_ipi_test >> KVM: selftests: use BITS_PER_TYPE() for NUMA masks >> KVM: selftests: add get_numa_mem_nodes() >> KVM: selftests: use allowed NUMA nodes in guest_memfd_test >> KVM: selftests: exercise guest_memfd folio migration >> >> > > Should I spin the independent patches out of this series for next cycle?
I'd say, yes :) -- Cheers, David
