Re: [PATCH v4 07/15] util/mmap-alloc: Factor out calculation of the pagesize for the guard page

["Murilo Opsfelder Araújo" <muriloo@linux.ibm.com>]

On Thursday, March 5, 2020 11:29:37 AM -03 David Hildenbrand wrote:
> Let's factor out calculating the size of the guard page and rename the
> variable to make it clearer that this pagesize only applies to the
> guard page.
>
> Reviewed-by: Peter Xu <peterx@redhat.com>
> Cc: "Michael S. Tsirkin" <mst@redhat.com>
> Cc: Murilo Opsfelder Araujo <muriloo@linux.ibm.com>
> Cc: Greg Kurz <groug@kaod.org>
> Cc: Eduardo Habkost <ehabkost@redhat.com>
> Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> Cc: Igor Mammedov <imammedo@redhat.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---

Acked-by: Murilo Opsfelder Araujo <muriloo@linux.ibm.com>

>  util/mmap-alloc.c | 31 ++++++++++++++++---------------
>  1 file changed, 16 insertions(+), 15 deletions(-)
>
> diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
> index 27dcccd8ec..f0277f9fad 100644
> --- a/util/mmap-alloc.c
> +++ b/util/mmap-alloc.c
> @@ -82,17 +82,27 @@ size_t qemu_mempath_getpagesize(const char *mem_path)
>      return qemu_real_host_page_size;
>  }
>
> +static inline size_t mmap_guard_pagesize(int fd)
> +{
> +#if defined(__powerpc64__) && defined(__linux__)
> +    /* Mappings in the same segment must share the same page size */
> +    return qemu_fd_getpagesize(fd);
> +#else
> +    return qemu_real_host_page_size;
> +#endif
> +}
> +
>  void *qemu_ram_mmap(int fd,
>                      size_t size,
>                      size_t align,
>                      bool shared,
>                      bool is_pmem)
>  {
> +    const size_t guard_pagesize = mmap_guard_pagesize(fd);
>      int flags;
>      int map_sync_flags = 0;
>      int guardfd;
>      size_t offset;
> -    size_t pagesize;
>      size_t total;
>      void *guardptr;
>      void *ptr;
> @@ -113,8 +123,7 @@ void *qemu_ram_mmap(int fd,
>       * anonymous memory is OK.
>       */
>      flags = MAP_PRIVATE;
> -    pagesize = qemu_fd_getpagesize(fd);
> -    if (fd == -1 || pagesize == qemu_real_host_page_size) {
> +    if (fd == -1 || guard_pagesize == qemu_real_host_page_size) {
>          guardfd = -1;
>          flags |= MAP_ANONYMOUS;
>      } else {
> @@ -123,7 +132,6 @@ void *qemu_ram_mmap(int fd,
>      }
>  #else
>      guardfd = -1;
> -    pagesize = qemu_real_host_page_size;
>      flags = MAP_PRIVATE | MAP_ANONYMOUS;
>  #endif
>
> @@ -135,7 +143,7 @@ void *qemu_ram_mmap(int fd,
>
>      assert(is_power_of_2(align));
>      /* Always align to host page size */
> -    assert(align >= pagesize);
> +    assert(align >= guard_pagesize);
>
>      flags = MAP_FIXED;
>      flags |= fd == -1 ? MAP_ANONYMOUS : 0;
> @@ -189,8 +197,8 @@ void *qemu_ram_mmap(int fd,
>       * a guard page guarding against potential buffer overflows.
>       */
>      total -= offset;
> -    if (total > size + pagesize) {
> -        munmap(ptr + size + pagesize, total - size - pagesize);
> +    if (total > size + guard_pagesize) {
> +        munmap(ptr + size + guard_pagesize, total - size - guard_pagesize);
> }
>
>      return ptr;
> @@ -198,15 +206,8 @@ void *qemu_ram_mmap(int fd,
>
>  void qemu_ram_munmap(int fd, void *ptr, size_t size)
>  {
> -    size_t pagesize;
> -
>      if (ptr) {
>          /* Unmap both the RAM block and the guard page */
> -#if defined(__powerpc64__) && defined(__linux__)
> -        pagesize = qemu_fd_getpagesize(fd);
> -#else
> -        pagesize = qemu_real_host_page_size;
> -#endif
> -        munmap(ptr, size + pagesize);
> +        munmap(ptr, size + mmap_guard_pagesize(fd));
>      }
>  }


--
Murilo