feat: checking the flags of the IA32_FEATURE_CONTROL MSR

proto/hypervisor.c

+#include "asm/msr.h"
 #include "linux/kern_levels.h"
+#include "linux/printk.h"
 #include <linux/init.h>   /* Needed for the macros */
 #include <linux/module.h> /* Needed by all modules */
 
-#define FEATURE_CONTROL_VMXON_ENABLED_OUTSIDE_SMX (1 << 2)
-#define FEATURE_CONTROL_LOCKED (1 << 0)
-#define MSR_IA32_FEATURE_CONTROL 0x0000003a
+#define IA32_FEATURE_CONTROL_LOCK_BIT (1 << 0)
+#define IA32_FEATURE_CONTROL_VMXON_IN_SMX (1 << 1)
+#define IA32_FEATURE_CONTROL_VMXON_OUTSIDE_SMX (1 << 2)
+#define IA32_FEATURE_CONTROL_MSR (0x3a)
 
 /*asm ( assembler template*/
 /*    : output operands                   (optional)*/
@@ -12,50 +15,12 @@
 /*    : clobbered registers list          (optional)*/
 /*    );*/
 
-static bool getVmxOperation(void) {
-    /*
-     * Configure IA32_FEATURE_CONTROL MSR to allow VMXON:
-     *  Bit 0: Lock bit. If clear, VMXON causes a #GP.
-     *  Bit 2: Enables VMXON outside of SMX operation. If clear, VMXON
-     *    outside of SMX causes a #GP.
-     */
-
-    unsigned long cr0, cr4;
-    unsigned long long required, feature_control;
-    unsigned long low1 = 0;
-    required = FEATURE_CONTROL_VMXON_ENABLED_OUTSIDE_SMX;
-    required |= FEATURE_CONTROL_LOCKED;
-    feature_control = __rdmsr(MSR_IA32_FEATURE_CONTROL);
-    printk(KERN_INFO "RDMS output is %ld\n", (long)feature_control);
-
-    if ((feature_control & required) != required) {
-        wrmsr(MSR_IA32_FEATURE_CONTROL, feature_control | required, low1);
-    }
-
-    /*
-     * Ensure bits in CR0 and CR4 are valid in VMX operation:
-     * - Bit X is 1 in _FIXED0: bit X is fixed to 1 in CRx.
-     * - Bit X is 0 in _FIXED1: bit X is fixed to 0 in CRx.
-     */
-    __asm__ volatile("mov %%cr0, %0" : "=r"(cr0) : : "memory");
-    cr0 &= __rdmsr(MSR_IA32_VMX_CR0_FIXED1);
-    cr0 |= __rdmsr(MSR_IA32_VMX_CR0_FIXED0);
-    __asm__ volatile("mov %0, %%cr0" : : "r"(cr0) : "memory");
-
-    __asm__ volatile("mov %%cr4, %0" : "=r"(cr4) : : "memory");
-    cr4 &= __rdmsr(MSR_IA32_VMX_CR4_FIXED1);
-    cr4 |= __rdmsr(MSR_IA32_VMX_CR4_FIXED0);
-    __asm__ volatile("mov %0, %%cr4" : : "r"(cr4) : "memory");
-
-    return true;
-}
-
 static void enable_vmx(void) {
     unsigned long cr4;
 
-    __asm__ volatile("mov %%cr4, %0" : "=r"(cr4)::"memory");
-    cr4 |= (1 << 13);
-    __asm__ volatile("mov %0, %%cr4" ::"r"(cr4) : "memory");
+    __asm__ volatile("mov %%cr4, %0" : "=r"(cr4));
+    cr4 |= (1UL << 13);
+    __asm__ volatile("mov %0, %%cr4" ::"r"(cr4));
 }
 
 static bool vmx_supported(void) {
@@ -68,6 +33,25 @@ static bool vmx_supported(void) {
     return (ecx >> 5) & 1;
 }
 
+static bool ia32_feature_control_flags(void) {
+    int msr_value = __rdmsr(IA32_FEATURE_CONTROL_MSR);
+
+    if (!(msr_value & IA32_FEATURE_CONTROL_LOCK_BIT)) {
+        printk(KERN_INFO "Writing to the IA32_FEATURE_CONTROL MSR\n");
+        __wrmsr(IA32_FEATURE_CONTROL_MSR,
+                IA32_FEATURE_CONTROL_LOCK_BIT |
+                    IA32_FEATURE_CONTROL_VMXON_OUTSIDE_SMX,
+                0);
+    }
+
+    if (!(msr_value & IA32_FEATURE_CONTROL_VMXON_OUTSIDE_SMX)) {
+        printk(KERN_INFO "Virtualization isn't available\n");
+        return false;
+    }
+
+    return true;
+}
+
 static int my_init(void) {
     if (!vmx_supported()) {
         printk(KERN_INFO "VMX isn't supported\n");
@@ -75,20 +59,24 @@ static int my_init(void) {
     }
 
     printk(KERN_INFO "VMX is supported!\n");
-
     enable_vmx();
-
     printk(KERN_INFO "VMX has been successfully enabled!\n");
 
-    if (!getVmxOperation()) {
-        printk(KERN_INFO "VMX operation couldn't correctly setup\n");
+    printk(KERN_INFO
+           "Check the necessary flags of the IA32_FEATURE_CONTROL_MSR\n");
+
+    if (!ia32_feature_control_flags()) {
+        printk(KERN_INFO "The flags of the IA32_FEATURE_CONTROL MSR do not "
+                         "permit virtualization\n");
         return -1;
     }
 
+    printk(KERN_INFO "IA32_FEATURE_CONTROL MSR flags allow virtualization\n");
+
     return 0;
 }
 
-static void my_exit(void) { printk(KERN_INFO "Goodbye world.\n"); }
+static void my_exit(void) { printk(KERN_INFO "Hypervisor has exited\n"); }
 
 module_init(my_init);
 module_exit(my_exit);