Performs version checking.

README.md
Describes new error (ENOPROTOOP) that results from a mismatch
between the loaded kernel module and what's in the batch request.

examples/example.c
Updated to use versioning.

msr_batch.c
Checks for correct version as part of batch request parsing.

msr_version.h
Bumped version to 2.0.0.

Tested on serif.

README.md

@@ -145,7 +145,8 @@ unheard-of.
 
 Starting in version 2.0.0, the __version__ field will be
 compared to the version of the loaded kernel module with a mismatch
-resulting in an error.  Earlier versions do not check this field.
+in the major version number resulting in an error.
+Earlier versions do not check this field.
 
 Each op is contained in a __struct msr_batch_op__:
 
@@ -292,17 +293,11 @@ Requested virtual CPU does not exist or is offline.
 ### /dev/cpu/msr_batch
 
 ### **ioctl(2)**
+Verifying the batch request can result in the following errors.
 
-All of the operations in the batch will be executed.  Each operation may result
-in an __EIO__, __ENXIO__, __EACCES__, or __EROFS__ error, which will be
-recorded in the __msr_batch_op__ struct.  If any operation caused an error, the
-first such error becomes the return value for **ioctl(2)**.
-
-__E2BIG__
-Kernel unable to allocate memory to hold the array of operations.
-
-__EACCES__
-An individual operation requested an MSR that is not present in the allowlist.
+__ENOTTY__
+Invalid ioctl command.  As of this writing the only ioctl command
+supported on this device is __X86_IOC_MSR_BATCH__, defined in __msr_safe.h__.
 
 __EBADF__
 The __msr_batch__ file was not opened for reading.
@@ -311,7 +306,25 @@ __EFAULT__
 Kernel **copy_from_user()** or **copy_to_user()** failed.
 
 __EINVAL__
-Number of requested batch operations is <=0.
+Number of requested batch operations is 0.
+
+__ENOPROTOOPT__
+There is a mismatch between the major version number of the currently-loaded
+msr-safe kernel module and the version number requested by the batch struct.
+
+__E2BIG__
+Kernel unable to allocate memory to hold the array of operations.
+
+__ENOMEM__
+Kernel unable to allocate memory to hold the results of __zalloc_cpumask_var()__.
+
+If all is well, all of the operations in the batch will be executed.  If an
+individual operation results in one of the following errors, the error will
+be recorded in its __msr_batch_op__ struct.  The first of these errors will
+become the return value for **ioctl(2)**.
+
+__EACCES__
+An individual operation requested an MSR that is not present in the allowlist.
 
 __EIO__
 A general protection fault occurred.  On Intel processors this
@@ -320,13 +333,6 @@ attempting to access a non-existent or reserved MSR address, c) writing 1-bits
 to a reserved area of an MSR, d) writing a non-canonical address to MSRs that
 take memory addresses, or e) writing to MSR bits that are marked as read-only.
 
-__ENOMEM__
-Kernel unable to allocate memory to hold the results of __zalloc_cpumask_var()__.
-
-__ENOTTY__
-Invalid ioctl command.  As of this writing the only ioctl command
-supported on this device is __X86_IOC_MSR_BATCH__, defined in __msr_safe.h__.
-
 __ENXIO__
 An individual operation requested a virtual CPU does not exist or is offline.
 

examples/example.c

@@ -26,13 +26,14 @@
 #include <stdlib.h>     // exit(3)
 #include <sys/ioctl.h>  // ioctl(2)
 
-#include "../msr_safe.h"   // batch data structs
+#include "../msr_safe.h"   	// batch data structs
+#include "../msr_version.h"	// MSR_SAFE_VERSION_u32
 
 #define MSR_MPERF 0xE7
 
 char const *const allowlist = "0xE7 0xFFFFFFFFFFFFFFFF\n";  // MPERF
 
-static uint8_t const nCPUs = 32;
+static uint8_t const nCPUs = 16;
 
 void set_allowlist()
 {
@@ -74,7 +75,7 @@ void measure_serial_latency()
 
     // Show results
     printf("Serial cycles from first write to last read:"
-           "%"PRIu64" (on %"PRIu8" CPUs)\n",
+           "%9"PRIu64" (on %"PRIu8" CPUs)\n",
            data[nCPUs - 1], nCPUs);
 }
 
@@ -95,7 +96,8 @@ void measure_batch_latency()
         r_ops[i].msr = w_ops[i].msr = MSR_MPERF;
         w_ops[i].msrdata = 0;
     }
-    rbatch.numops = wbatch.numops = nCPUs;
+    rbatch.numops  = wbatch.numops  = nCPUs;
+    rbatch.version = wbatch.version = MSR_SAFE_VERSION_u32;
     rbatch.ops = r_ops;
     wbatch.ops = w_ops;
 
@@ -104,8 +106,8 @@ void measure_batch_latency()
     rc = ioctl(fd, X86_IOC_MSR_BATCH, &rbatch);
     assert(-1 != rc);
 
-    printf("Batch cycles from first write to last read:"
-           "%llu (on %"PRIu8" CPUs)\n",
+    printf("Batch cycles from first write to last read: "
+           "%9llu (on %"PRIu8" CPUs)\n",
            r_ops[nCPUs - 1].msrdata, nCPUs);
 }
 

msr_batch.c

@@ -33,6 +33,7 @@
 #include "msr_safe.h"
 #include "msr-smp.h"
 #include "msr_allowlist.h"
+#include "msr_version.h"
 
 static struct class *cdev_class;
 static char cdev_created;
@@ -102,12 +103,20 @@ static long msrbatch_ioctl(struct file *f, unsigned int ioc, unsigned long arg)
         return -EFAULT;
     }
 
-    if (koa.numops <= 0)
+    if (koa.numops == 0)
     {
         pr_debug("Invalid # of ops %d\n", koa.numops);
         return -EINVAL;
     }
 
+    if ( ((koa.version >> 16) & 0xff) != MSR_SAFE_VERSION_MAJOR ){
+	pr_debug("Version mismatch: loaded is %d, requested is %d\n",
+			MSR_SAFE_VERSION_MAJOR,
+			(koa.version >> 16) & 0xff
+	);
+	return -ENOPROTOOPT;
+    }
+
     uops = koa.ops;
 
     koa.ops = kmalloc_array(koa.numops, sizeof(*koa.ops), GFP_KERNEL);

msr_version.h

@@ -22,8 +22,8 @@ int msr_version_init(int *majordev);
 
 void msr_version_cleanup(int majordev);
 
-#define MSR_SAFE_VERSION_MAJOR 1
-#define MSR_SAFE_VERSION_MINOR 8
+#define MSR_SAFE_VERSION_MAJOR 2
+#define MSR_SAFE_VERSION_MINOR 0
 #define MSR_SAFE_VERSION_PATCH 0
 
 #define MSR_SAFE_VERSION_u32 ( \