Commit 7197fb40 authored by Michael S. Tsirkin's avatar Michael S. Tsirkin
Browse files

util/mmap-alloc: fix hugetlb support on ppc64 



Since commit 8561c924 "exec: allocate PROT_NONE pages on top of
RAM", it is no longer possible to back guest RAM with hugepages on ppc64
hosts:

mmap(NULL, 285212672, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) =
0x3fff57000000
mmap(0x3fff57000000, 268435456, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED, 19, 0) = -1 EBUSY (Device or resource busy)

This is because on ppc64, Linux fixes a page size for a virtual address
at mmap time, so we can't switch a range of memory from anonymous
small pages to hugetlbs with MAP_FIXED.

See commit d0f13e3c20b6fb73ccb467bdca97fa7cf5a574cd
("[POWERPC] Introduce address space "slices"") in Linux
history for the details.

Detect this and create the PROT_NONE mapping using the same fd.

Naturally, this makes the guard page bigger with hugetlbfs.

Based on patch by Greg Kurz.

Acked-by: default avatarRik van Riel <riel@redhat.com>
Reviewed-by: default avatarGreg Kurz <gkurz@linux.vnet.ibm.com>
Tested-by: default avatarGreg Kurz <gkurz@linux.vnet.ibm.com>
Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
parent 0560b0e9

include/qemu/mmap-alloc.h

+2 −0
Original line number Diff line number Diff line
@@ -3,6 +3,8 @@ 


#include "qemu-common.h"



size_t qemu_fd_getpagesize(int fd);



void *qemu_ram_mmap(int fd, size_t size, size_t align, bool shared);



void qemu_ram_munmap(void *ptr, size_t size);

util/mmap-alloc.c

+39 −0
Original line number Diff line number Diff line
@@ -14,6 +14,32 @@ 
#include <sys/mman.h>

#include <assert.h>



#define HUGETLBFS_MAGIC       0x958458f6



#ifdef CONFIG_LINUX

#include <sys/vfs.h>

#endif



size_t qemu_fd_getpagesize(int fd)

{

#ifdef CONFIG_LINUX

    struct statfs fs;

    int ret;



    if (fd != -1) {

        do {

            ret = fstatfs(fd, &fs);

        } while (ret != 0 && errno == EINTR);



        if (ret == 0 && fs.f_type == HUGETLBFS_MAGIC) {

            return fs.f_bsize;

        }

    }

#endif



    return getpagesize();

}



void *qemu_ram_mmap(int fd, size_t size, size_t align, bool shared)

{

    /*
@@ -21,7 +47,20 @@ void *qemu_ram_mmap(int fd, size_t size, size_t align, bool shared) 
     * space, even if size is already aligned.

     */

    size_t total = size + align;

#if defined(__powerpc64__) && defined(__linux__)

    /* On ppc64 mappings in the same segment (aka slice) must share the same

     * page size. Since we will be re-allocating part of this segment

     * from the supplied fd, we should make sure to use the same page size,

     * unless we are using the system page size, in which case anonymous memory

     * is OK. Use align as a hint for the page size.

     * In this case, set MAP_NORESERVE to avoid allocating backing store memory.

     */

    int anonfd = fd == -1 || qemu_fd_getpagesize(fd) == getpagesize() ? -1 : fd;

    int flags = anonfd == -1 ? MAP_ANONYMOUS : MAP_NORESERVE;

    void *ptr = mmap(0, total, PROT_NONE, flags | MAP_PRIVATE, anonfd, 0);

#else

    void *ptr = mmap(0, total, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);

#endif

    size_t offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr;

    void *ptr1;

util/oslib-posix.c

+1 −23
Original line number Diff line number Diff line
@@ -46,7 +46,6 @@ extern int daemon(int, int); 
#else

#  define QEMU_VMALLOC_ALIGN getpagesize()

#endif

#define HUGETLBFS_MAGIC       0x958458f6



#include <termios.h>

#include <unistd.h>
@@ -65,7 +64,6 @@ extern int daemon(int, int); 


#ifdef CONFIG_LINUX

#include <sys/syscall.h>

#include <sys/vfs.h>

#endif



#ifdef __FreeBSD__
@@ -340,26 +338,6 @@ static void sigbus_handler(int signal) 
    siglongjmp(sigjump, 1);

}



static size_t fd_getpagesize(int fd)

{

#ifdef CONFIG_LINUX

    struct statfs fs;

    int ret;



    if (fd != -1) {

        do {

            ret = fstatfs(fd, &fs);

        } while (ret != 0 && errno == EINTR);



        if (ret == 0 && fs.f_type == HUGETLBFS_MAGIC) {

            return fs.f_bsize;

        }

    }

#endif



    return getpagesize();

}



void os_mem_prealloc(int fd, char *area, size_t memory)

{

    int ret;
@@ -387,7 +365,7 @@ void os_mem_prealloc(int fd, char *area, size_t memory) 
        exit(1);

    } else {

        int i;

        size_t hpagesize = fd_getpagesize(fd);

        size_t hpagesize = qemu_fd_getpagesize(fd);

        size_t numpages = DIV_ROUND_UP(memory, hpagesize);



        /* MAP_POPULATE silently ignores failures */