Re: [PULL 02/14] os: add an ability to lock memory on_fault

[Stefan Hajnoczi <stefanha@gmail.com>]

On Tue, Feb 11, 2025 at 5:52 PM Peter Xu <peterx@redhat.com> wrote:
>
> From: Daniil Tatianin <d-tatianin@yandex-team.ru>
>
> This will be used in the following commits to make it possible to only
> lock memory on fault instead of right away.

Hi Peter and Daniil,
Please take a look at this CI failure:
https://gitlab.com/qemu-project/qemu/-/jobs/9117106042#L3603

Thanks,
Stefan

>
> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
> Reviewed-by: Peter Xu <peterx@redhat.com>
> Signed-off-by: Daniil Tatianin <d-tatianin@yandex-team.ru>
> Link: https://lore.kernel.org/r/20250123131944.391886-2-d-tatianin@yandex-team.ru
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>  include/system/os-posix.h |  2 +-
>  include/system/os-win32.h |  3 ++-
>  migration/postcopy-ram.c  |  2 +-
>  os-posix.c                | 10 ++++++++--
>  system/vl.c               |  2 +-
>  5 files changed, 13 insertions(+), 6 deletions(-)
>
> diff --git a/include/system/os-posix.h b/include/system/os-posix.h
> index b881ac6c6f..ce5b3bccf8 100644
> --- a/include/system/os-posix.h
> +++ b/include/system/os-posix.h
> @@ -53,7 +53,7 @@ bool os_set_runas(const char *user_id);
>  void os_set_chroot(const char *path);
>  void os_setup_limits(void);
>  void os_setup_post(void);
> -int os_mlock(void);
> +int os_mlock(bool on_fault);
>
>  /**
>   * qemu_alloc_stack:
> diff --git a/include/system/os-win32.h b/include/system/os-win32.h
> index b82a5d3ad9..cd61d69e10 100644
> --- a/include/system/os-win32.h
> +++ b/include/system/os-win32.h
> @@ -123,8 +123,9 @@ static inline bool is_daemonized(void)
>      return false;
>  }
>
> -static inline int os_mlock(void)
> +static inline int os_mlock(bool on_fault)
>  {
> +    (void)on_fault;
>      return -ENOSYS;
>  }
>
> diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
> index 6a6da6ba7f..fc4d8a10df 100644
> --- a/migration/postcopy-ram.c
> +++ b/migration/postcopy-ram.c
> @@ -652,7 +652,7 @@ int postcopy_ram_incoming_cleanup(MigrationIncomingState *mis)
>      }
>
>      if (enable_mlock) {
> -        if (os_mlock() < 0) {
> +        if (os_mlock(false) < 0) {
>              error_report("mlock: %s", strerror(errno));
>              /*
>               * It doesn't feel right to fail at this point, we have a valid
> diff --git a/os-posix.c b/os-posix.c
> index 9cce55ff2f..48afb2990d 100644
> --- a/os-posix.c
> +++ b/os-posix.c
> @@ -327,18 +327,24 @@ void os_set_line_buffering(void)
>      setvbuf(stdout, NULL, _IOLBF, 0);
>  }
>
> -int os_mlock(void)
> +int os_mlock(bool on_fault)
>  {
>  #ifdef HAVE_MLOCKALL
>      int ret = 0;
> +    int flags = MCL_CURRENT | MCL_FUTURE;
>
> -    ret = mlockall(MCL_CURRENT | MCL_FUTURE);
> +    if (on_fault) {
> +        flags |= MCL_ONFAULT;
> +    }
> +
> +    ret = mlockall(flags);
>      if (ret < 0) {
>          error_report("mlockall: %s", strerror(errno));
>      }
>
>      return ret;
>  #else
> +    (void)on_fault;
>      return -ENOSYS;
>  #endif
>  }
> diff --git a/system/vl.c b/system/vl.c
> index 9c6942c6cf..e94fc7ea35 100644
> --- a/system/vl.c
> +++ b/system/vl.c
> @@ -797,7 +797,7 @@ static QemuOptsList qemu_run_with_opts = {
>  static void realtime_init(void)
>  {
>      if (enable_mlock) {
> -        if (os_mlock() < 0) {
> +        if (os_mlock(false) < 0) {
>              error_report("locking memory failed");
>              exit(1);
>          }
> --
> 2.47.0
>
>