When shrinking a mmap we want to re-reserve the already populated area.
When growing a memory region, we want to populate starting with a given
fd_offset. Prepare by allowing to pass these parameters.
Also, let's make sure we always process full pages, to avoid
unmapping/remapping pages that are already in use when
growing/shrinking. (existing callers seem to guarantee this, but that's
not obvious)
Cc: "Michael S. Tsirkin" <m...@redhat.com>
Cc: Greg Kurz <gr...@kaod.org>
Cc: Murilo Opsfelder Araujo <muri...@linux.ibm.com>
Cc: Eduardo Habkost <ehabk...@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilb...@redhat.com>
Signed-off-by: David Hildenbrand <da...@redhat.com>
---
util/mmap-alloc.c | 32 +++++++++++++++++++++-----------
1 file changed, 21 insertions(+), 11 deletions(-)
diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
index f043ccb0ab..63ad6893b7 100644
--- a/util/mmap-alloc.c
+++ b/util/mmap-alloc.c
@@ -83,12 +83,12 @@ size_t qemu_mempath_getpagesize(const char *mem_path)
}
/*
- * Reserve a new memory region of the requested size to be used for mapping
- * from the given fd (if any).
+ * Reserve a new memory region of the requested size or re-reserve parts
+ * of an existing region to be used for mapping from the given fd (if any).
*/
-static void *mmap_reserve(size_t size, int fd)
+static void *mmap_reserve(void *ptr, size_t size, int fd)
{
- int flags = MAP_PRIVATE;
+ int flags = MAP_PRIVATE | (ptr ? MAP_FIXED : 0);
#if defined(__powerpc64__) && defined(__linux__)
/*
@@ -111,19 +111,23 @@ static void *mmap_reserve(size_t size, int fd)
flags |= MAP_ANONYMOUS;
#endif
- return mmap(0, size, PROT_NONE, flags, fd, 0);
+ return mmap(ptr, size, PROT_NONE, flags, fd, 0);
}
/*
* Populate memory in a reserved region from the given fd (if any).
*/
-static void *mmap_populate(void *ptr, size_t size, int fd, bool shared,
- bool is_pmem)
+static void *mmap_populate(void *ptr, size_t size, int fd, size_t fd_offset,
+ bool shared, bool is_pmem)
{
int map_sync_flags = 0;
int flags = MAP_FIXED;
void *new_ptr;
+ if (fd == -1) {
+ fd_offset = 0;
+ }
+
flags |= fd == -1 ? MAP_ANONYMOUS : 0;
flags |= shared ? MAP_SHARED : MAP_PRIVATE;
if (shared && is_pmem) {
@@ -131,7 +135,7 @@ static void *mmap_populate(void *ptr, size_t size, int fd,
bool shared,
}
new_ptr = mmap(ptr, size, PROT_READ | PROT_WRITE, flags | map_sync_flags,
- fd, 0);
+ fd, fd_offset);
if (new_ptr == MAP_FAILED && map_sync_flags) {
if (errno == ENOTSUP) {
char *proc_link = g_strdup_printf("/proc/self/fd/%d", fd);
@@ -153,7 +157,7 @@ static void *mmap_populate(void *ptr, size_t size, int fd,
bool shared,
* If mmap failed with MAP_SHARED_VALIDATE | MAP_SYNC, we will try
* again without these flags to handle backwards compatibility.
*/
- new_ptr = mmap(ptr, size, PROT_READ | PROT_WRITE, flags, fd, 0);
+ new_ptr = mmap(ptr, size, PROT_READ | PROT_WRITE, flags, fd,
fd_offset);
}
return new_ptr;
}
@@ -178,13 +182,16 @@ void *qemu_ram_mmap(int fd,
size_t offset, total;
void *ptr, *guardptr;
+ /* we can only map whole pages */
+ size = QEMU_ALIGN_UP(size, pagesize);
+
/*
* Note: this always allocates at least one extra page of virtual address
* space, even if size is already aligned.
*/
total = size + align;
- guardptr = mmap_reserve(total, fd);
+ guardptr = mmap_reserve(0, total, fd);
if (guardptr == MAP_FAILED) {
return MAP_FAILED;
}
@@ -195,7 +202,7 @@ void *qemu_ram_mmap(int fd,
offset = QEMU_ALIGN_UP((uintptr_t)guardptr, align) - (uintptr_t)guardptr;
- ptr = mmap_populate(guardptr + offset, size, fd, shared, is_pmem);
+ ptr = mmap_populate(guardptr + offset, size, fd, 0, shared, is_pmem);
if (ptr == MAP_FAILED) {
munmap(guardptr, total);
return MAP_FAILED;
@@ -221,6 +228,9 @@ void qemu_ram_munmap(int fd, void *ptr, size_t size)
{
const size_t pagesize = mmap_pagesize(fd);
+ /* we can only map whole pages */
+ size = QEMU_ALIGN_UP(size, pagesize);
+
if (ptr) {
/* Unmap both the RAM block and the guard page */
munmap(ptr, size + pagesize);
--
2.24.1
