diff options
| author | Fuad Tabba <tabba@google.com> | 2025-07-29 15:54:41 -0700 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2025-08-27 04:35:00 -0400 |
| commit | a12578e1477cbfb547256ed8dee6d5142a59cdcd (patch) | |
| tree | 553f8758f34d9aadb2ac56831bf57f9080fe0c76 /arch | |
| parent | d1e54dd08f163a9021433020d16a8f8f70ddc41c (diff) | |
KVM: guest_memfd: Add plumbing to host to map guest_memfd pages
Introduce the core infrastructure to enable host userspace to mmap()
guest_memfd-backed memory. This is needed for several evolving KVM use
cases:
* Non-CoCo VM backing: Allows VMMs like Firecracker to run guests
entirely backed by guest_memfd, even for non-CoCo VMs [1]. This
provides a unified memory management model and simplifies guest memory
handling.
* Direct map removal for enhanced security: This is an important step
for direct map removal of guest memory [2]. By allowing host userspace
to fault in guest_memfd pages directly, we can avoid maintaining host
kernel direct maps of guest memory. This provides additional hardening
against Spectre-like transient execution attacks by removing a
potential attack surface within the kernel.
* Future guest_memfd features: This also lays the groundwork for future
enhancements to guest_memfd, such as supporting huge pages and
enabling in-place sharing of guest memory with the host for CoCo
platforms that permit it [3].
Enable the basic mmap and fault handling logic within guest_memfd, but
hold off on allow userspace to actually do mmap() until the architecture
support is also in place.
[1] https://github.com/firecracker-microvm/firecracker/tree/feature/secret-hiding
[2] https://lore.kernel.org/linux-mm/cc1bb8e9bc3e1ab637700a4d3defeec95b55060a.camel@amazon.com
[3] https://lore.kernel.org/all/c1c9591d-218a-495c-957b-ba356c8f8e09@redhat.com/T/#u
Reviewed-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Shivank Garg <shivankg@amd.com>
Acked-by: David Hildenbrand <david@redhat.com>
Co-developed-by: Ackerley Tng <ackerleytng@google.com>
Signed-off-by: Ackerley Tng <ackerleytng@google.com>
Signed-off-by: Fuad Tabba <tabba@google.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20250729225455.670324-11-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/kvm/x86.c | 11 |
1 files changed, 11 insertions, 0 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 604490b1cb19..33fba801b205 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -13521,6 +13521,16 @@ bool kvm_arch_no_poll(struct kvm_vcpu *vcpu) } EXPORT_SYMBOL_GPL(kvm_arch_no_poll); +#ifdef CONFIG_KVM_GUEST_MEMFD +/* + * KVM doesn't yet support mmap() on guest_memfd for VMs with private memory + * (the private vs. shared tracking needs to be moved into guest_memfd). + */ +bool kvm_arch_supports_gmem_mmap(struct kvm *kvm) +{ + return !kvm_arch_has_private_mem(kvm); +} + #ifdef CONFIG_HAVE_KVM_ARCH_GMEM_PREPARE int kvm_arch_gmem_prepare(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn, int max_order) { @@ -13534,6 +13544,7 @@ void kvm_arch_gmem_invalidate(kvm_pfn_t start, kvm_pfn_t end) kvm_x86_call(gmem_invalidate)(start, end); } #endif +#endif int kvm_spec_ctrl_test_value(u64 value) { |