[RFC PATCH v1 2/5] vm_planes: Add VBS VTL call handling and plane memory sealing

Wire up the VBS inter-plane communication and memory protection
infrastructure on the QEMU side.

Memory sealing (plane activate path):
  After plane-1 boots and its vCPU threads are running, seal
  plane-1's memory from plane-0 access:
  1. Issue KVM_SET_PLANE_MEMORY_ATTRIBUTES to set NO_WRITE|NO_EXEC
     on plane-0's EPT for the GPA range occupied by plane-1.
  2. Clear ps->host_addr so QEMU userspace can no longer access
     the region.

VBS VTL hypercall handler:
  Handle KVM_HC_VBS_VTL_CALL (hypercall 15) exits from the guest.
  The plane-0 VBS subsystem passes the GPA of a shared calling-area
  (CAA) page; QEMU reads the call_id from the page, logs it, and
  returns -ENOSYS for now (plane-1 responder not yet implemented).
  Enable the hypercall in kvm_enable_hypercall() alongside the
  existing VM planes hypercalls.

Header sync:
  - linux-headers/linux/kvm.h: Add KVM_MEMORY_ATTRIBUTE_NO_WRITE,
    KVM_MEMORY_ATTRIBUTE_NO_EXEC, struct kvm_plane_memory_attributes,
    and KVM_SET_PLANE_MEMORY_ATTRIBUTES ioctl definition.
  - include/standard-headers/linux/kvm_para.h: Add KVM_HC_VBS_VTL_CALL.

(cherry picked from commit 414016c40ec8226b0f5d4cbd5eed0589b7c1689e)
---
 linux-headers/linux/kvm.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/linux-headers/linux/kvm.h b/linux-headers/linux/kvm.h
index d66ce6d272..9dbd3824e9 100644
--- a/linux-headers/linux/kvm.h
+++ b/linux-headers/linux/kvm.h
@@ -1653,6 +1653,19 @@ struct kvm_memory_attributes {
 };
 
 #define KVM_MEMORY_ATTRIBUTE_PRIVATE           (1ULL << 3)
+#define KVM_MEMORY_ATTRIBUTE_NO_WRITE          (1ULL << 4)
+#define KVM_MEMORY_ATTRIBUTE_NO_EXEC           (1ULL << 5)
+
+/* Set memory attributes on a specific plane's address space. */
+struct kvm_plane_memory_attributes {
+	__u32 plane;
+	__u32 flags;
+	__u64 address;
+	__u64 size;
+	__u64 attributes;
+};
+
+#define KVM_SET_PLANE_MEMORY_ATTRIBUTES	_IOW(KVMIO, 0xd6, struct kvm_plane_memory_attributes)
 
 #define KVM_MEMORY_ATTRIBUTE_NO_WRITE          (1ULL << 4)
 #define KVM_MEMORY_ATTRIBUTE_NO_EXEC           (1ULL << 5)
-- 
2.55.0