On Thursday, March 5, 2020 11:29:40 AM -03 David Hildenbrand wrote:
> When shrinking a mmap we want to re-reserve the already activated area.
> When growing a memory region, we want to activate 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. Add some asserts.
>
> Reviewed-by: Richard Henderson <richard.hender...@linaro.org>
> Reviewed-by: Peter Xu <pet...@redhat.com>
> Cc: Igor Kotrasinski <i.kotrasi...@partner.samsung.com>
> Cc: Murilo Opsfelder Araujo <muri...@linux.ibm.com>
> 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>
> Cc: Igor Mammedov <imamm...@redhat.com>
> Signed-off-by: David Hildenbrand <da...@redhat.com>
> ---
Acked-by: Murilo Opsfelder Araujo <muri...@linux.ibm.com>
> util/mmap-alloc.c | 34 +++++++++++++++++++++++-----------
> 1 file changed, 23 insertions(+), 11 deletions(-)
>
> diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
> index 8f40ef4fed..2767caa33b 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 activated 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__)
> /*
> @@ -111,20 +111,24 @@ 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);
> }
>
> /*
> * Activate memory in a reserved region from the given fd (if any), to make
> * it accessible.
> */
> -static void *mmap_activate(void *ptr, size_t size, int fd, bool shared,
> - bool is_pmem)
> +static void *mmap_activate(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 *activated_ptr;
>
> + if (fd == -1) {
> + fd_offset = 0;
> + }
> +
> flags |= fd == -1 ? MAP_ANONYMOUS : 0;
> flags |= shared ? MAP_SHARED : MAP_PRIVATE;
> if (shared && is_pmem) {
> @@ -132,7 +136,7 @@ static void *mmap_activate(void *ptr, size_t size, int
> fd, bool shared, }
>
> activated_ptr = mmap(ptr, size, PROT_READ | PROT_WRITE,
> - flags | map_sync_flags, fd, 0);
> + flags | map_sync_flags, fd, fd_offset);
> if (activated_ptr == MAP_FAILED && map_sync_flags) {
> if (errno == ENOTSUP) {
> char *proc_link = g_strdup_printf("/proc/self/fd/%d", fd);
> @@ -154,7 +158,8 @@ static void *mmap_activate(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. */
> - activated_ptr = mmap(ptr, size, PROT_READ | PROT_WRITE, flags, fd,
> 0); + activated_ptr = mmap(ptr, size, PROT_READ | PROT_WRITE, flags,
> fd, + fd_offset);
> }
> return activated_ptr;
> }
> @@ -176,16 +181,19 @@ void *qemu_ram_mmap(int fd,
> bool is_pmem)
> {
> const size_t guard_pagesize = mmap_guard_pagesize(fd);
> + const size_t pagesize = qemu_fd_getpagesize(fd);
> size_t offset, total;
> void *ptr, *guardptr;
>
> + g_assert(QEMU_IS_ALIGNED(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(NULL, total, fd);
> if (guardptr == MAP_FAILED) {
> return MAP_FAILED;
> }
> @@ -196,7 +204,7 @@ void *qemu_ram_mmap(int fd,
>
> offset = QEMU_ALIGN_UP((uintptr_t)guardptr, align) -
> (uintptr_t)guardptr;
>
> - ptr = mmap_activate(guardptr + offset, size, fd, shared, is_pmem);
> + ptr = mmap_activate(guardptr + offset, size, fd, 0, shared, is_pmem);
> if (ptr == MAP_FAILED) {
> munmap(guardptr, total);
> return MAP_FAILED;
> @@ -220,6 +228,10 @@ void *qemu_ram_mmap(int fd,
>
> void qemu_ram_munmap(int fd, void *ptr, size_t size)
> {
> + const size_t pagesize = qemu_fd_getpagesize(fd);
> +
> + g_assert(QEMU_IS_ALIGNED(size, pagesize));
> +
> if (ptr) {
> /* Unmap both the RAM block and the guard page */
> munmap(ptr, size + mmap_guard_pagesize(fd));
--
Murilo
