Re: [Qemu-devel] [PATCH v2] exec.c: Ensure right alignment also for file backed ram

[Paolo Bonzini]

On 07/04/2016 23:31, Dominik Dingel wrote:
> diff --git a/exec.c b/exec.c
> index c4f9036..1ae98e4 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -1241,6 +1241,7 @@ static void *file_ram_alloc(RAMBlock *block,
>      void *area;
>      int fd = -1;
>      int64_t page_size;
> +    int64_t alignment;
>  
>      if (kvm_enabled() && !kvm_has_sync_mmu()) {
>          error_setg(errp,
> @@ -1296,7 +1297,8 @@ static void *file_ram_alloc(RAMBlock *block,
>      }
>  
>      page_size = qemu_fd_getpagesize(fd);
> -    block->mr->align = page_size;
> +    alignment = MAX(page_size, QEMU_VMALLOC_ALIGN);
> +    block->mr->align = alignment;
>  
>      if (memory < page_size) {
>          error_setg(errp, "memory size 0x" RAM_ADDR_FMT " must be equal to "
> @@ -1305,7 +1307,7 @@ static void *file_ram_alloc(RAMBlock *block,
>          goto error;
>      }
>  
> -    memory = ROUND_UP(memory, page_size);
> +    memory = ROUND_UP(memory, alignment);

I think this change is not necessary either; it is enough to change the
qemu_ram_mmap below.

Paolo

>      /*
>       * ftruncate is not supported by hugetlbfs in older
> @@ -1317,7 +1319,7 @@ static void *file_ram_alloc(RAMBlock *block,
>          perror("ftruncate");
>      }
>  
> -    area = qemu_ram_mmap(fd, memory, page_size, block->flags & RAM_SHARED);
> +    area = qemu_ram_mmap(fd, memory, alignment, block->flags & RAM_SHARED);
>      if (area == MAP_FAILED) {
>          error_setg_errno(errp, errno,
>                           "unable to map backing store for guest RAM");
> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> index 408783f..a472372 100644
> --- a/include/qemu/osdep.h
> +++ b/include/qemu/osdep.h
> @@ -247,6 +247,18 @@ void qemu_anon_ram_free(void *ptr, size_t size);
>  
>  #endif
>  
> +#if defined(__linux__) && (defined(__x86_64__) || defined(__arm__))
> +   /* Use 2 MiB alignment so transparent hugepages can be used by KVM.
> +      Valgrind does not support alignments larger than 1 MiB,
> +      therefore we need special code which handles running on Valgrind. */
> +#  define QEMU_VMALLOC_ALIGN (512 * 4096)
> +#elif defined(__linux__) && defined(__s390x__)
> +   /* Use 1 MiB (segment size) alignment so gmap can be used by KVM. */
> +#  define QEMU_VMALLOC_ALIGN (256 * 4096)
> +#else
> +#  define QEMU_VMALLOC_ALIGN getpagesize()
> +#endif
> +
>  int qemu_madvise(void *addr, size_t len, int advice);
>  
>  int qemu_open(const char *name, int flags, ...);
> diff --git a/util/oslib-posix.c b/util/oslib-posix.c
> index 20ca141..4adde93 100644
> --- a/util/oslib-posix.c
> +++ b/util/oslib-posix.c
> @@ -26,18 +26,6 @@
>   * THE SOFTWARE.
>   */
>  
> -#if defined(__linux__) && (defined(__x86_64__) || defined(__arm__))
> -   /* Use 2 MiB alignment so transparent hugepages can be used by KVM.
> -      Valgrind does not support alignments larger than 1 MiB,
> -      therefore we need special code which handles running on Valgrind. */
> -#  define QEMU_VMALLOC_ALIGN (512 * 4096)
> -#elif defined(__linux__) && defined(__s390x__)
> -   /* Use 1 MiB (segment size) alignment so gmap can be used by KVM. */
> -#  define QEMU_VMALLOC_ALIGN (256 * 4096)
> -#else
> -#  define QEMU_VMALLOC_ALIGN getpagesize()
> -#endif
> -
>  #include "qemu/osdep.h"
>  #include <termios.h>
>  #include <termios.h>
>