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author | Michael S. Tsirkin <mst@redhat.com> | 2015-09-24 14:41:17 +0300 |
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committer | Michael S. Tsirkin <mst@redhat.com> | 2015-10-21 09:24:44 +0300 |
commit | 794e8f301a17953efa78ab7538019ec43c59e82a (patch) | |
tree | 99efbb84259d79552bd700c58242f6350b88efd2 /util/mmap-alloc.c | |
parent | 7df953bd456da45f761064974820ab5c3fd7b2aa (diff) | |
download | hqemu-794e8f301a17953efa78ab7538019ec43c59e82a.zip hqemu-794e8f301a17953efa78ab7538019ec43c59e82a.tar.gz |
exec: factor out duplicate mmap code
Anonymous and file-backed RAM allocation are now almost exactly the same.
Reduce code duplication by moving RAM mmap code out of oslib-posix.c and
exec.c.
Reported-by: Marc-André Lureau <mlureau@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Tested-by: Thibaut Collet <thibaut.collet@6wind.com>
Diffstat (limited to 'util/mmap-alloc.c')
-rw-r--r-- | util/mmap-alloc.c | 71 |
1 files changed, 71 insertions, 0 deletions
diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c new file mode 100644 index 0000000..1394269 --- /dev/null +++ b/util/mmap-alloc.c @@ -0,0 +1,71 @@ +/* + * Support for RAM backed by mmaped host memory. + * + * Copyright (c) 2015 Red Hat, Inc. + * + * Authors: + * Michael S. Tsirkin <mst@redhat.com> + * + * This work is licensed under the terms of the GNU GPL, version 2 or + * later. See the COPYING file in the top-level directory. + */ +#include <qemu/mmap-alloc.h> +#include <sys/types.h> +#include <sys/mman.h> +#include <assert.h> + +void *qemu_ram_mmap(int fd, size_t size, size_t align, bool shared) +{ + /* + * Note: this always allocates at least one extra page of virtual address + * space, even if size is already aligned. + */ + size_t total = size + align; + void *ptr = mmap(0, total, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0); + size_t offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr; + void *ptr1; + + if (ptr == MAP_FAILED) { + return NULL; + } + + /* Make sure align is a power of 2 */ + assert(!(align & (align - 1))); + /* Always align to host page size */ + assert(align >= getpagesize()); + + ptr1 = mmap(ptr + offset, size, PROT_READ | PROT_WRITE, + MAP_FIXED | + (fd == -1 ? MAP_ANONYMOUS : 0) | + (shared ? MAP_SHARED : MAP_PRIVATE), + fd, 0); + if (ptr1 == MAP_FAILED) { + munmap(ptr, total); + return NULL; + } + + ptr += offset; + total -= offset; + + if (offset > 0) { + munmap(ptr - offset, offset); + } + + /* + * Leave a single PROT_NONE page allocated after the RAM block, to serve as + * a guard page guarding against potential buffer overflows. + */ + if (total > size + getpagesize()) { + munmap(ptr + size + getpagesize(), total - size - getpagesize()); + } + + return ptr; +} + +void qemu_ram_munmap(void *ptr, size_t size) +{ + if (ptr) { + /* Unmap both the RAM block and the guard page */ + munmap(ptr, size + getpagesize()); + } +} |