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Message-ID: <cover.1760731772.git.ackerleytng@google.com>
Date: Fri, 17 Oct 2025 13:11:41 -0700
From: Ackerley Tng <ackerleytng@...gle.com>
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Subject: [RFC PATCH v1 00/37] guest_memfd: In-place conversion support
Hello,
IIUC this is the first independent patch series for guest_memfd's in-place
conversion series! Happy to finally bring this out on its own.
Previous versions of this feature, part of other series, are available at
[1][2][3].
Many prior discussions have led up to these main features of this series, and
these are the main points I'd like feedback on.
1. Having private/shared status stored in a maple tree (Thanks Michael for your
support of using maple trees over xarrays for performance! [4]).
2. Having a new guest_memfd ioctl (not a vm ioctl) that performs conversions.
3. Using ioctls/structs/input attribute similar to the existing vm ioctl
KVM_SET_MEMORY_ATTRIBUTES to perform conversions.
4. Storing requested attributes directly in the maple tree.
5. Using a KVM module-wide param to toggle between setting memory attributes via
vm and guest_memfd ioctls (making them mututally exclusive - a single loaded
KVM module can only do one of the two.)
6. Skipping LRU in guest_memfd folios - make guest_memfd folios not participate
in LRU to avoid LRU refcounts from interfering with conversions.
This series is based on kvm/next, followed by
+ v12 of NUMA mempolicy support patches [5]
+ 3 cleanup patches from Sean [6][7][8]
Everything is stitched together here for your convenience
https://github.com/googleprodkernel/linux-cc/commits/guest_memfd-inplace-conversion-v1
Thank you all for helping with this series!
If I missed out your comment from a previous series, it's not intentional!
Please do raise it again.
TODOs:
+ There might be an issue with memory failure handling because when guest_memfd
folios stop participating in LRU. From a preliminary analysis,
HWPoisonHandlable() is only true if PageLRU() is true. This needs further
investigation.
[1] https://lore.kernel.org/all/bd163de3118b626d1005aa88e71ef2fb72f0be0f.1726009989.git.ackerleytng@google.com/
[2] https://lore.kernel.org/all/20250117163001.2326672-6-tabba@google.com/
[3] https://lore.kernel.org/all/b784326e9ccae6a08388f1bf39db70a2204bdc51.1747264138.git.ackerleytng@google.com/
[4] https://lore.kernel.org/all/20250529054227.hh2f4jmyqf6igd3i@amd.com/
[5] https://lore.kernel.org/all/20251007221420.344669-1-seanjc@google.com/T/
[6] https://lore.kernel.org/all/20250924174255.2141847-1-seanjc@google.com/
[7] https://lore.kernel.org/all/20251007224515.374516-1-seanjc@google.com/
[8] https://lore.kernel.org/all/20251007223625.369939-1-seanjc@google.com/
Ackerley Tng (19):
KVM: guest_memfd: Update kvm_gmem_populate() to use gmem attributes
KVM: Introduce KVM_SET_MEMORY_ATTRIBUTES2
KVM: guest_memfd: Don't set FGP_ACCESSED when getting folios
KVM: guest_memfd: Skip LRU for guest_memfd folios
KVM: guest_memfd: Add support for KVM_SET_MEMORY_ATTRIBUTES
KVM: selftests: Update framework to use KVM_SET_MEMORY_ATTRIBUTES2
KVM: selftests: guest_memfd: Test basic single-page conversion flow
KVM: selftests: guest_memfd: Test conversion flow when INIT_SHARED
KVM: selftests: guest_memfd: Test indexing in guest_memfd
KVM: selftests: guest_memfd: Test conversion before allocation
KVM: selftests: guest_memfd: Convert with allocated folios in
different layouts
KVM: selftests: guest_memfd: Test precision of conversion
KVM: selftests: guest_memfd: Test that truncation does not change
shared/private status
KVM: selftests: guest_memfd: Test conversion with elevated page
refcount
KVM: selftests: Reset shared memory after hole-punching
KVM: selftests: Provide function to look up guest_memfd details from
gpa
KVM: selftests: Make TEST_EXPECT_SIGBUS thread-safe
KVM: selftests: Update private_mem_conversions_test to mmap()
guest_memfd
KVM: selftests: Add script to exercise private_mem_conversions_test
Sean Christopherson (18):
KVM: guest_memfd: Introduce per-gmem attributes, use to guard user
mappings
KVM: Rename KVM_GENERIC_MEMORY_ATTRIBUTES to KVM_VM_MEMORY_ATTRIBUTES
KVM: Enumerate support for PRIVATE memory iff kvm_arch_has_private_mem
is defined
KVM: Stub in ability to disable per-VM memory attribute tracking
KVM: guest_memfd: Wire up kvm_get_memory_attributes() to per-gmem
attributes
KVM: guest_memfd: Enable INIT_SHARED on guest_memfd for x86 Coco VMs
KVM: Move KVM_VM_MEMORY_ATTRIBUTES config definition to x86
KVM: Let userspace disable per-VM mem attributes, enable per-gmem
attributes
KVM: selftests: Create gmem fd before "regular" fd when adding memslot
KVM: selftests: Rename guest_memfd{,_offset} to gmem_{fd,offset}
KVM: selftests: Add support for mmap() on guest_memfd in core library
KVM: selftests: Add helpers for calling ioctls on guest_memfd
KVM: selftests: guest_memfd: Test that shared/private status is
consistent across processes
KVM: selftests: Add selftests global for guest memory attributes
capability
KVM: selftests: Provide common function to set memory attributes
KVM: selftests: Check fd/flags provided to mmap() when setting up
memslot
KVM: selftests: Update pre-fault test to work with per-guest_memfd
attributes
KVM: selftests: Update private memory exits test work with per-gmem
attributes
Documentation/virt/kvm/api.rst | 72 ++-
arch/x86/include/asm/kvm_host.h | 2 +-
arch/x86/kvm/Kconfig | 15 +-
arch/x86/kvm/mmu/mmu.c | 4 +-
arch/x86/kvm/x86.c | 13 +-
include/linux/kvm_host.h | 44 +-
include/trace/events/kvm.h | 4 +-
include/uapi/linux/kvm.h | 17 +
mm/filemap.c | 1 +
mm/memcontrol.c | 2 +
tools/testing/selftests/kvm/.gitignore | 1 +
tools/testing/selftests/kvm/Makefile.kvm | 1 +
.../kvm/guest_memfd_conversions_test.c | 498 ++++++++++++++++++
.../testing/selftests/kvm/include/kvm_util.h | 127 ++++-
.../testing/selftests/kvm/include/test_util.h | 29 +-
tools/testing/selftests/kvm/lib/kvm_util.c | 128 +++--
tools/testing/selftests/kvm/lib/test_util.c | 7 -
.../selftests/kvm/pre_fault_memory_test.c | 2 +-
.../kvm/x86/private_mem_conversions_test.c | 55 +-
.../kvm/x86/private_mem_conversions_test.py | 159 ++++++
.../kvm/x86/private_mem_kvm_exits_test.c | 36 +-
virt/kvm/Kconfig | 4 +-
virt/kvm/guest_memfd.c | 414 +++++++++++++--
virt/kvm/kvm_main.c | 104 +++-
24 files changed, 1554 insertions(+), 185 deletions(-)
create mode 100644 tools/testing/selftests/kvm/guest_memfd_conversions_test.c
create mode 100755 tools/testing/selftests/kvm/x86/private_mem_conversions_test.py
--
2.51.0.858.gf9c4a03a3a-goog
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