Re: [Qemu-devel] [PATCH 4/4] mm: sys_remap_anon_pages

[Andrea Arcangeli]

On Mon, May 06, 2013 at 09:57:01PM +0200, Andrea Arcangeli wrote:
> ===
> 
> static unsigned char *c, *tmp;
> 
> void userfault_sighandler(int signum, siginfo_t *info, void *ctx)

oops, the hash of the test program got cut... so I append it below
which is nicer without leading whitespaces.

===
#define _GNU_SOURCE
#include <sys/mman.h>
#include <pthread.h>
#include <strings.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <signal.h>
#include <sys/syscall.h>
#include <sys/types.h>

#define USE_USERFAULT
#define THP

#define MADV_USERFAULT  18

#define SIZE (1024*1024*1024)

#define SYS_remap_anon_pages 314

static unsigned char *c, *tmp;

void userfault_sighandler(int signum, siginfo_t *info, void *ctx)
{
        unsigned char *addr = info->si_addr;
        int len = 4096;
        int ret;

#ifdef THP
        addr = (unsigned char *) ((unsigned long) addr & ~((2*1024*1024)-1));
        len = 2*1024*1024;
#endif
        if (addr >= c && addr < c + SIZE) {
                unsigned long offset = addr - c;
                ret = syscall(SYS_remap_anon_pages, c+offset, tmp+offset, len);
                if (ret)
                        perror("sigbus remap_anon_pages"), exit(1);
                //printf("sigbus offset %lu\n", offset);
                return;
        }

        printf("sigbus error addr %p c %p tmp %p\n", addr, c, tmp), exit(1);
}

int main()
{
        struct sigaction sa;
        int ret;
        unsigned long i;
#ifndef THP
        /*
         * Fails with THP due lack of alignment because of memset
         * pre-filling the destination
         */
        c = mmap(0, SIZE, PROT_READ|PROT_WRITE,
                 MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
        if (c == MAP_FAILED)
                perror("mmap"), exit(1);
        tmp = mmap(0, SIZE, PROT_READ|PROT_WRITE,
                   MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
        if (tmp == MAP_FAILED)
                perror("mmap"), exit(1);
#else
        ret = posix_memalign((void **)&c, 2*1024*1024, SIZE);
        if (ret)
                perror("posix_memalign"), exit(1);
        ret = posix_memalign((void **)&tmp, 2*1024*1024, SIZE);
        if (ret)
                perror("posix_memalign"), exit(1);
#endif
        /*
         * MADV_USERFAULT must run before memset, to avoid THP 2m
         * faults to map memory into "tmp", if "tmp" isn't allocated
         * with hugepage alignment.
         */
        if (madvise(c, SIZE, MADV_USERFAULT))
                perror("madvise"), exit(1);
        memset(tmp, 0xaa, SIZE);

        sa.sa_sigaction = userfault_sighandler;
        sigemptyset(&sa.sa_mask);
        sa.sa_flags = SA_SIGINFO;
        sigaction(SIGBUS, &sa, NULL);

#ifndef USE_USERFAULT
        ret = syscall(SYS_remap_anon_pages, c, tmp, SIZE);
        if (ret)
                perror("remap_anon_pages"), exit(1);
#endif

        for (i = 0; i < SIZE; i += 4096) {
                if ((i/4096) % 2) {
                        /* exercise read and write MADV_USERFAULT */
                        c[i+1] = 0xbb;
                }
                if (c[i] != 0xaa)
                        printf("error %x offset %lu\n", c[i], i), exit(1);
        }

        return 0;
}