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Message-ID: <87b10d94-dca2-4ecb-a86f-b38c5c90e0cf@redhat.com>
Date: Wed, 27 Aug 2025 10:43:54 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>, Marc Zyngier <maz@...nel.org>,
Oliver Upton <oliver.upton@...ux.dev>
Cc: kvm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
kvmarm@...ts.linux.dev, linux-kernel@...r.kernel.org,
Ira Weiny <ira.weiny@...el.com>, Gavin Shan <gshan@...hat.com>,
Shivank Garg <shivankg@....com>, Vlastimil Babka <vbabka@...e.cz>,
Xiaoyao Li <xiaoyao.li@...el.com>, David Hildenbrand <david@...hat.com>,
Fuad Tabba <tabba@...gle.com>, Ackerley Tng <ackerleytng@...gle.com>,
Tao Chan <chentao@...inos.cn>, James Houghton <jthoughton@...gle.com>
Subject: Re: [PATCH v17 00/24] KVM: Enable mmap() for guest_memfd
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@amazon.co.uk
> [3] https://lore.kernel.org/all/20250328153133.3504118-1-tabba@google.com
>
> 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@google.com
> - 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@google.com
> - 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@google.com
> - 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
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