On 7/30/25 00:54, Sean Christopherson wrote:
Paolo,
The arm64 patches have been Reviewed-by Marc, and AFAICT the x86 side of
things is a go. Barring a screwup on my end, this just needs your approval.
Assuming everything looks good, it'd be helpful to get this into kvm/next
shortly after rc1. The x86 Kconfig changes in particular create semantic
conflicts with in-flight series.
Add support for host userspace mapping of guest_memfd-backed memory for VM
types that do NOT use support KVM_MEMORY_ATTRIBUTE_PRIVATE (which isn't
precisely the same thing as CoCo VMs, since x86's SEV-MEM and SEV-ES have
no way to detect private vs. shared).
mmap() support paves the way for several evolving KVM use cases:
* Allows VMMs like Firecracker to run guests entirely backed by
guest_memfd [1]. This provides a unified memory management model for
both confidential and non-confidential guests, simplifying VMM design.
* Enhanced Security via direct map removal: When combined with Patrick's
series for direct map removal [2], this provides additional hardening
against Spectre-like transient execution attacks by eliminating the
need for host kernel direct maps of guest memory.
* Lays the groundwork for *restricted* mmap() support for guest_memfd-backed
memory on CoCo platforms [3] that permit in-place
sharing of guest memory with the host.
Based on kvm/queue.
Applied to kvm/next, thanks!
Paolo
[1] https://github.com/firecracker-microvm/firecracker/tree/feature/secret-hiding
[2] https://lore.kernel.org/all/20250221160728.1584559-1-roypat@xxxxxxxxxxxx
[3] https://lore.kernel.org/all/20250328153133.3504118-1-tabba@xxxxxxxxxx
v17:
- Collect reviews. [Xiaoyao, David H.]
- Write a better changelog for the CONFIG_KVM_GENERIC_PRIVATE_MEM =>
CONFIG_HAVE_KVM_ARCH_GMEM_POPULATE rename. [Xiaoyao]
- Correctly gmem_max_mapping_level()'s '0' return in the right patch. [Xiaoyao]
- Replace call to kvm_gmem_get_pfn() with a WARN_ONCE() in the hugepage
recovery path. [Ackerley]
- Add back "KVM: x86/mmu: Handle guest page faults for guest_memfd with
shared memory". [Ackerley]
- Rework the selftest flags testcase to query MMAP support for a given VM
type instead of hardcoding expectations in the test. [Sean]
- Add a testcase to verify KVM can map guest_memfd memory into the guest
even if the userspace address in the memslot isn't (properly) mmap'd. [Sean]
v16:
- https://lore.kernel.org/all/20250723104714.1674617-1-tabba@xxxxxxxxxx
- Rework and simplify Kconfig selection and dependencies.
- Always enable guest_memfd for KVM x86 (64-bit) and arm64, which
simplifies the enablement checks.
- Based on kvm-x86/next: commit 33f843444e28 ("Merge branch 'vmx'").
v15:
- https://lore.kernel.org/all/20250717162731.446579-1-tabba@xxxxxxxxxx
- Removed KVM_SW_PROTECTED_VM dependency on KVM_GENERIC_GMEM_POPULATE
- Fixed some commit messages
v14:
- https://lore.kernel.org/all/20250715093350.2584932-1-tabba@xxxxxxxxxx
- Fixed handling of guest faults in case of invalidation in arm64
- Handle VNCR_EL2-triggered faults backed by guest_memfd (arm64 nested
virt)
- Applied suggestions from latest feedback
- Rebase on Linux 6.16-rc6
Ackerley Tng (2):
KVM: x86/mmu: Rename .private_max_mapping_level() to
.gmem_max_mapping_level()
KVM: x86/mmu: Handle guest page faults for guest_memfd with shared
memory
Fuad Tabba (15):
KVM: Rename CONFIG_KVM_PRIVATE_MEM to CONFIG_KVM_GUEST_MEMFD
KVM: Rename CONFIG_KVM_GENERIC_PRIVATE_MEM to
CONFIG_HAVE_KVM_ARCH_GMEM_POPULATE
KVM: Rename kvm_slot_can_be_private() to kvm_slot_has_gmem()
KVM: Fix comments that refer to slots_lock
KVM: Fix comment that refers to kvm uapi header path
KVM: x86: Enable KVM_GUEST_MEMFD for all 64-bit builds
KVM: guest_memfd: Add plumbing to host to map guest_memfd pages
KVM: guest_memfd: Track guest_memfd mmap support in memslot
KVM: arm64: Refactor user_mem_abort()
KVM: arm64: Handle guest_memfd-backed guest page faults
KVM: arm64: nv: Handle VNCR_EL2-triggered faults backed by guest_memfd
KVM: arm64: Enable support for guest_memfd backed memory
KVM: Allow and advertise support for host mmap() on guest_memfd files
KVM: selftests: Do not use hardcoded page sizes in guest_memfd test
KVM: selftests: guest_memfd mmap() test when mmap is supported
Sean Christopherson (7):
KVM: x86: Have all vendor neutral sub-configs depend on KVM_X86, not
just KVM
KVM: x86: Select KVM_GENERIC_PRIVATE_MEM directly from
KVM_SW_PROTECTED_VM
KVM: x86: Select TDX's KVM_GENERIC_xxx dependencies iff
CONFIG_KVM_INTEL_TDX=y
KVM: x86/mmu: Hoist guest_memfd max level/order helpers "up" in mmu.c
KVM: x86/mmu: Enforce guest_memfd's max order when recovering
hugepages
KVM: x86/mmu: Extend guest_memfd's max mapping level to shared
mappings
KVM: selftests: Add guest_memfd testcase to fault-in on !mmap()'d
memory
Documentation/virt/kvm/api.rst | 9 +
arch/arm64/kvm/Kconfig | 1 +
arch/arm64/kvm/mmu.c | 203 +++++++++++----
arch/arm64/kvm/nested.c | 41 ++-
arch/x86/include/asm/kvm-x86-ops.h | 2 +-
arch/x86/include/asm/kvm_host.h | 6 +-
arch/x86/kvm/Kconfig | 26 +-
arch/x86/kvm/mmu/mmu.c | 142 ++++++-----
arch/x86/kvm/mmu/mmu_internal.h | 2 +-
arch/x86/kvm/mmu/tdp_mmu.c | 2 +-
arch/x86/kvm/svm/sev.c | 6 +-
arch/x86/kvm/svm/svm.c | 2 +-
arch/x86/kvm/svm/svm.h | 4 +-
arch/x86/kvm/vmx/main.c | 7 +-
arch/x86/kvm/vmx/tdx.c | 5 +-
arch/x86/kvm/vmx/x86_ops.h | 2 +-
arch/x86/kvm/x86.c | 11 +
include/linux/kvm_host.h | 38 +--
include/uapi/linux/kvm.h | 2 +
tools/testing/selftests/kvm/Makefile.kvm | 1 +
.../testing/selftests/kvm/guest_memfd_test.c | 236 ++++++++++++++++--
virt/kvm/Kconfig | 15 +-
virt/kvm/Makefile.kvm | 2 +-
virt/kvm/guest_memfd.c | 81 +++++-
virt/kvm/kvm_main.c | 12 +-
virt/kvm/kvm_mm.h | 4 +-
26 files changed, 648 insertions(+), 214 deletions(-)
base-commit: beafd7ecf2255e8b62a42dc04f54843033db3d24
