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#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>

struct pagemaps {
    unsigned long long  pfn:55;
    unsigned long long  pgshift:6; /* legacy */
    unsigned long long  rsvd:1;
    unsigned long long  swapped:1;
    unsigned long long  present:1;
};

static int pagesize;

static unsigned long long vtop(unsigned long long addr)
{
    struct pagemaps pinfo;
    unsigned int pinfo_size = sizeof(pinfo);
    int pagesize = getpagesize();
    unsigned long long offset = addr / pagesize * pinfo_size;
    int fd, pgmask;
    const char *pagemapname = "/proc/self/pagemap";

    fd = open(pagemapname, O_RDONLY);
    if (fd == -1) {
        perror(pagemapname);
        return 0;
    }
    if (pread(fd, (void *)&pinfo, pinfo_size, offset) != pinfo_size) {
        perror(pagemapname);
        close(fd);
        return 0;
    }
    close(fd);
    pgmask = pagesize - 1;
    return (pinfo.pfn * pagesize) | (addr & pgmask);
}

int main()
{
    unsigned long long gpa;
    void *buf;

    pagesize = getpagesize();

    /*
     * First, allocate one page at least, so that we can ensure at
     * least one page is completely owned by this process.
     *
     * Second, if you are going to allocate only one page, do not use
     * malloc()/calloc()/... that do not make any promise on the
     * alignment. If you are going to allocate more than one page,
     * remember to find a page-aligned address in the allocated space.
     */
    buf = mmap(NULL, pagesize, PROT_READ | PROT_WRITE | PROT_EXEC,
               MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
    if ( buf == MAP_FAILED ) {
        perror("Failed to allocate memory");
        return -1;
    }
    assert(!((unsigned long long)buf & (pagesize - 1)));
    /*
     * Write to the buffer to ensure a physical page is really
     * allocated and mapped. Otherwise, vtop below may fail.
     */
    memset(buf, 0xcc, pagesize);

    printf("gva=0x%p\n", buf);

    /* translate GVA to GPA */
    gpa = vtop((unsigned long long)buf);
    printf("gpa=0x%llx\n", gpa);

    /* keep the GPA is valid. */
    while(1) {
        sleep(1);
    }
    return 1;
}