Shared Memory between Kernel and User - memory-management

Question

I am currently working on a kernel module for a RaspberryPi 3 and am new to this area. This should generate an interrupt on a rising or falling edge. In the corresponding ISR, a time stamp is set and a signal is generated to notify a user application.
I have taken the signaling for the sake of the code.
My goal is now to write the value of the time stamp into a shared memory and the user application can read it out after an incoming signal in order to measure the latency between the interrupt and the signal received in the user application. I have already researched but found no solution. How do I map the virtual kernel address of the allocated memory into the user application and what steps are necessary?
Thanks in advance.
Kernel Code:
/****************************************************************************/
/* Kernelmodul Shared Memory */
/****************************************************************************/
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/gpio.h>
#include <linux/types.h>
#include <linux/ioport.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
// kmalloc
#include <linux/slab.h>
// ioremap
#include <asm/io.h>
/****************************************************************************/
/* Define block */
/****************************************************************************/
#define DriverAuthor ""
#define DriverDescription "Shared Memory"
#define InterruptPin 26
#define GPIO_PIN_DEV_STR "PIN"
#define GPIO_PIN_STR "Timestamp"
unsigned int * timerAddr;
unsigned int time = 0;
unsigned int * SHMvirtual = 0;
/****************************************************************************/
/* Module params declaration block */
/****************************************************************************/
static short int gpio_pin = InterruptPin;
/****************************************************************************/
/* Interrupts variables block */
/****************************************************************************/
short int irq_gpio_pin = InterruptPin;
short int irq_enabled = 0; // this is only a flag
/****************************************************************************/
/* IRQ handler */
/****************************************************************************/
static irqreturn_t ISR(int irq, void *dev_id, struct pt_regs *regs) {
unsigned long flags;
// disable hard interrupts (remember them in flag 'flags')
local_irq_save(flags);
time = timerAddr[1];
*SHMvirtual = time;
// restore hard interrupts
local_irq_restore(flags);
return IRQ_HANDLED;
}
/****************************************************************************/
/* This function configures interrupts. */
/****************************************************************************/
void configInterrupts(void) {
if (gpio_request(gpio_pin, GPIO_PIN_STR))
{
printk(KERN_INFO "GPIO request faiure %d\n", gpio_pin);
return;
}
if ( (irq_gpio_pin = gpio_to_irq(gpio_pin)) < 0 )
{
printk(KERN_INFO "GPIO to IRQ mapping faiure %d\n", gpio_pin);
return;
}
printk(KERN_INFO "Mapped int %d\n", irq_gpio_pin);
if (request_irq(irq_gpio_pin, (irq_handler_t ) ISR, (IRQF_TRIGGER_FALLING | IRQF_TRIGGER_RISING), GPIO_PIN_STR,
GPIO_PIN_DEV_STR))
{
printk("Interrupt Request failure\n");
return;
}
return;
}
/****************************************************************************/
/* This function releases interrupts. */
/****************************************************************************/
void releaseInterrupt(void) {
free_irq(irq_gpio_pin, GPIO_PIN_DEV_STR);
gpio_free(gpio_pin);
return;
}
/****************************************************************************/
/* Module init / cleanup block. */
/****************************************************************************/
int initModule(void) {
printk(KERN_INFO "Hello\n");
configInterrupts();
timerAddr = ioremap(0x3F003000, 0x20);
SHMvirtual = (unsigned int *)kmalloc(sizeof(time),GFP_USER);
return 0;
}
void cleanupModule(void) {
printk(KERN_INFO "Goodbye\n");
releaseInterrupt();
kfree(SHMvirtual);
return;
}
module_init(initModule);
module_exit(cleanupModule);
/****************************************************************************/
/* Module licensing/description block. */
/****************************************************************************/
MODULE_LICENSE("GPL");
MODULE_AUTHOR(DriverAuthor);
MODULE_DESCRIPTION(DriverDescription);