From a32409cc7bcb32087199882f671fa3d0cdcea276 Mon Sep 17 00:00:00 2001
From: Nick Rogers <1903140+rogersnm@users.noreply.github.com>
Date: Sat, 15 Aug 2026 15:20:23 +0000
Subject: [PATCH] Expose VmFd::enable_cap on all architectures

The KVM_ENABLE_CAP vm ioctl is architecture independent, but both the
ioctl definition and VmFd::enable_cap were compiled only for x86_64,
s390x and powerpc. aarch64 now needs them: Linux 6.15 gates writes to
the implementation ID registers (MIDR_EL1, REVIDR_EL1, AIDR_EL1) behind
KVM_CAP_ARM_WRITABLE_IMP_ID_REGS, which a VMM must enable on the VM
before creating vCPUs. Without enable_cap, VMMs fall back to issuing
the raw ioctl themselves (see firecracker-microvm/firecracker#6116).

Remove the cfg gates and guard the x86 specific portion of the doc
example so it builds and runs on every architecture.

Signed-off-by: Nick Rogers <1903140+rogersnm@users.noreply.github.com>
---
 kvm-ioctls/CHANGELOG.md      | 9 +++++++++
 kvm-ioctls/src/ioctls/vm.rs  | 2 +-
 kvm-ioctls/src/kvm_ioctls.rs | 1 -
 3 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/kvm-ioctls/CHANGELOG.md b/kvm-ioctls/CHANGELOG.md
index e0fd7430..42956c48 100644
--- a/kvm-ioctls/CHANGELOG.md
+++ b/kvm-ioctls/CHANGELOG.md
@@ -2,6 +2,15 @@
 
 ## Upcoming Release
 
+### Changed
+
+- [[#382]](https://github.com/rust-vmm/kvm/pull/382) `VmFd::enable_cap` and the
+  `KVM_ENABLE_CAP` ioctl definition are now available on all architectures
+  instead of only x86_64, s390x and powerpc. aarch64 needs them to enable
+  `KVM_CAP_ARM_WRITABLE_IMP_ID_REGS` (Linux 6.15), without which writes to the
+  implementation ID registers (for example `MIDR_EL1` through a VMM CPU
+  template) fail with EINVAL.
+
 ## v0.25.0
 
 ### Added
diff --git a/kvm-ioctls/src/ioctls/vm.rs b/kvm-ioctls/src/ioctls/vm.rs
index 466dd8ff..3e5f7b99 100644
--- a/kvm-ioctls/src/ioctls/vm.rs
+++ b/kvm-ioctls/src/ioctls/vm.rs
@@ -1521,9 +1521,9 @@ impl VmFd {
     /// // Because an IOAPIC supports 24 pins, that's the reason why this test
     /// // picked this number as reference.
     /// cap.args[0] = 24;
+    /// #[cfg(target_arch = "x86_64")]
     /// vm.enable_cap(&cap).unwrap();
     /// ```
-    #[cfg(any(target_arch = "x86_64", target_arch = "s390x", target_arch = "powerpc"))]
     pub fn enable_cap(&self, cap: &kvm_enable_cap) -> Result<()> {
         // SAFETY: The ioctl is safe because we allocated the struct and we know the
         // kernel will write exactly the size of the struct.
diff --git a/kvm-ioctls/src/kvm_ioctls.rs b/kvm-ioctls/src/kvm_ioctls.rs
index b294c57e..af802307 100644
--- a/kvm-ioctls/src/kvm_ioctls.rs
+++ b/kvm-ioctls/src/kvm_ioctls.rs
@@ -226,7 +226,6 @@ ioctl_io_nr!(KVM_SET_TSC_KHZ, KVMIO, 0xa2);
 ioctl_io_nr!(KVM_GET_TSC_KHZ, KVMIO, 0xa3);
 
 /* Available with KVM_CAP_ENABLE_CAP */
-#[cfg(not(any(target_arch = "aarch64", target_arch = "riscv64")))]
 ioctl_iow_nr!(KVM_ENABLE_CAP, KVMIO, 0xa3, kvm_enable_cap);
 /* Available with KVM_CAP_SIGNAL_MSI */
 #[cfg(any(