NVIDIA: SAUCE: target/arm: Add sysfs detection for KVM CCA capability

target/arm/aarch64-qmp-cmds.c

@@ -37,8 +37,9 @@ CcaCapability *qmp_query_cca_capabilities(Error **errp)
     }
 
     /*
-     * Use the runtime-detected KVM_CAP_ARM_RME value to handle
-     * the ABI change between kernel versions (243 on 6.16, 244 on later).
+     * Use kvm_arm_rme_get_cap() to get the KVM CCA capability value
+     * from the kernel's sysfs module parameter, handling ABI changes
+     * between kernel versions gracefully.
      */
     if (!kvm_check_extension(kvm_state, kvm_arm_rme_get_cap())) {
         error_setg(errp, "RME is not enabled in KVM");

target/arm/kvm-rme.c

@@ -24,27 +24,64 @@
 #include <sys/utsname.h>
 
 /*
- * Returns the correct KVM_CAP_ARM_RME capability value for the running kernel.
- * This handles the ABI change between kernel versions:
- *   - Linux 6.16: KVM_CAP_ARM_RME == 243
- *   - Linux 6.17+: KVM_CAP_ARM_RME == 244
+ * Sysfs paths for KVM CCA capability detection.
+ * v11+ host patches (6.18+) use RMI naming, v10 (6.17) uses RME naming.
+ */
+#define KVM_CAP_ARM_RMI_SYSFS_PATH "/sys/module/kvm/parameters/kvm_cap_arm_rmi"
+#define KVM_CAP_ARM_RME_SYSFS_PATH "/sys/module/kvm/parameters/kvm_cap_arm_rme"
+
+/*
+ * Returns the correct KVM CCA capability value for the running kernel.
+ *
+ * The ARM CCA host patches underwent a naming change from RME to RMI in v11:
+ *   - v10 (Linux 6.17): KVM_CAP_ARM_RME, sysfs param kvm_cap_arm_rme
+ *   - v11 (Linux 6.18+): KVM_CAP_ARM_RMI, sysfs param kvm_cap_arm_rmi
+ *
+ * Detection order:
+ *   1. Try reading from the v11 sysfs module parameter (RMI naming):
+ *        /sys/module/kvm/parameters/kvm_cap_arm_rmi
+ *
+ *   2. Try reading from the v10 sysfs module parameter (RME naming):
+ *        /sys/module/kvm/parameters/kvm_cap_arm_rme
+ *
+ *   3. Fall back to uname-based detection for Linux 6.16 dev kernel
+ *      (which does not have the sysfs parameter): capability == 243
+ *
+ *   4. Otherwise use the compile-time KVM_CAP_ARM_RME value.
  */
 unsigned int kvm_arm_rme_get_cap(void)
 {
     static unsigned int rme_cap = 0;
     static bool detected = false;
 
     if (!detected) {
-        struct utsname buf;
-        int major, minor;
+        FILE *f = NULL;
+        int cap;
 
         rme_cap = KVM_CAP_ARM_RME;
 
-        if (uname(&buf) == 0) {
-            if (sscanf(buf.release, "%d.%d", &major, &minor) == 2) {
-                /* For Linux kernel v6.16, KVM_CAP_ARM_RME == 243 */
-                if ((major == 6) && (minor == 16)) {
-                    rme_cap = 243;
+        /* First try v11 sysfs path (RMI naming, 6.18+ kernels) */
+        f = fopen(KVM_CAP_ARM_RMI_SYSFS_PATH, "r");
+        if (!f) {
+            /* Then try v10 sysfs path (RME naming, 6.17 kernels) */
+            f = fopen(KVM_CAP_ARM_RME_SYSFS_PATH, "r");
+        }
+
+        if (f) {
+            if (fscanf(f, "%d", &cap) == 1 && cap > 0) {
+                rme_cap = cap;
+            }
+            fclose(f);
+        } else {
+            /* Fallback for 6.16 dev kernel (no sysfs parameter) */
+            struct utsname buf;
+            int major, minor;
+
+            if (uname(&buf) == 0) {
+                if (sscanf(buf.release, "%d.%d", &major, &minor) == 2) {
+                    if (major == 6 && minor == 16) {
+                        rme_cap = 243;
+                    }
                 }
             }
         }

target/arm/kvm_arm.h

@@ -277,9 +277,16 @@ void arm_cpu_kvm_set_irq(void *arm_cpu, int irq, int level);
 /**
  * kvm_arm_rme_get_cap:
  *
- * Returns the correct KVM_CAP_ARM_RME capability value for the running
- * kernel. This handles the ABI change between kernel versions where the
- * capability number differs (e.g., 243 on kernel 6.16, 244 on later kernels).
+ * Returns the correct KVM CCA capability value for the running kernel.
+ * Supports both v10 (RME naming, 6.17) and v11+ (RMI naming, 6.18+) host patches.
+ *
+ * First tries to read from the sysfs module parameters:
+ *   /sys/module/kvm/parameters/kvm_cap_arm_rmi  (v11+, 6.18+)
+ *   /sys/module/kvm/parameters/kvm_cap_arm_rme  (v10, 6.17)
+ *
+ * Falls back to uname-based kernel version detection (6.16=243, 6.17=244,
+ * 6.18=246) if sysfs is not available, or uses the compile-time
+ * KVM_CAP_ARM_RME value as a last resort.
  */
 unsigned int kvm_arm_rme_get_cap(void);