diff mbox series

[v12,16/18] KVM: Introduce the KVM capability KVM_CAP_GMEM_SHARED_MEM

Message ID 20250611133330.1514028-17-tabba@google.com
State New
Headers show
Series KVM: Mapping guest_memfd backed memory at the host for software protected VMs | expand

Commit Message

Fuad Tabba June 11, 2025, 1:33 p.m. UTC 
This patch introduces the KVM capability KVM_CAP_GMEM_SHARED_MEM, which
indicates that guest_memfd supports shared memory (when enabled by the
flag). This support is limited to certain VM types, determined per
architecture.

This patch also updates the KVM documentation with details on the new
capability, flag, and other information about support for shared memory
in guest_memfd.

Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Signed-off-by: Fuad Tabba <tabba@google.com>
---
 Documentation/virt/kvm/api.rst | 9 +++++++++
 include/uapi/linux/kvm.h       | 1 +
 virt/kvm/kvm_main.c            | 4 ++++
 3 files changed, 14 insertions(+)
diff mbox series

Patch

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 1bd2d42e6424..4ef3d8482000 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6407,6 +6407,15 @@  most one mapping per page, i.e. binding multiple memory regions to a single
 guest_memfd range is not allowed (any number of memory regions can be bound to
 a single guest_memfd file, but the bound ranges must not overlap).
 
+When the capability KVM_CAP_GMEM_SHARED_MEM is supported, the 'flags' field
+supports GUEST_MEMFD_FLAG_SUPPORT_SHARED.  Setting this flag on guest_memfd
+creation enables mmap() and faulting of guest_memfd memory to host userspace.
+
+When the KVM MMU performs a PFN lookup to service a guest fault and the backing
+guest_memfd has the GUEST_MEMFD_FLAG_SUPPORT_SHARED set, then the fault will
+always be consumed from guest_memfd, regardless of whether it is a shared or a
+private fault.
+
 See KVM_SET_USER_MEMORY_REGION2 for additional details.
 
 4.143 KVM_PRE_FAULT_MEMORY
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index cb19150fd595..c74cf8f73337 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -934,6 +934,7 @@  struct kvm_enable_cap {
 #define KVM_CAP_ARM_EL2 240
 #define KVM_CAP_ARM_EL2_E2H0 241
 #define KVM_CAP_RISCV_MP_STATE_RESET 242
+#define KVM_CAP_GMEM_SHARED_MEM 243
 
 struct kvm_irq_routing_irqchip {
 	__u32 irqchip;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index d41bcc6a78b0..441c9b53b876 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4913,6 +4913,10 @@  static int kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
 #ifdef CONFIG_KVM_GMEM
 	case KVM_CAP_GUEST_MEMFD:
 		return !kvm || kvm_arch_supports_gmem(kvm);
+#endif
+#ifdef CONFIG_KVM_GMEM_SHARED_MEM
+	case KVM_CAP_GMEM_SHARED_MEM:
+		return !kvm || kvm_arch_supports_gmem_shared_mem(kvm);
 #endif
 	default:
 		break;