Re: [PATCH v2 6/7] migration/postcopy: Use uffd helpers

[Peter Xu <peterx@redhat.com>]

On Thu, Sep 19, 2024 at 02:46:25PM +0100, dave@treblig.org wrote:
> From: "Dr. David Alan Gilbert" <dave@treblig.org>
> 
> Use the uffd_copy_page, uffd_zero_page and uffd_wakeup helpers
> rather than calling ioctl ourselves.
> 
> They return -errno on error, and print an error_report themselves.
> I think this actually makes postcopy_place_page actually more
> consistent in it's callers.
> 
> Signed-off-by: Dr. David Alan Gilbert <dave@treblig.org>
> ---
>  migration/postcopy-ram.c | 47 +++++++++++-----------------------------
>  1 file changed, 13 insertions(+), 34 deletions(-)
> 
> diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
> index 1c374b7ea1..e2b318d3da 100644
> --- a/migration/postcopy-ram.c
> +++ b/migration/postcopy-ram.c
> @@ -746,18 +746,9 @@ int postcopy_wake_shared(struct PostCopyFD *pcfd,
>                           RAMBlock *rb)
>  {
>      size_t pagesize = qemu_ram_pagesize(rb);
> -    struct uffdio_range range;
> -    int ret;
>      trace_postcopy_wake_shared(client_addr, qemu_ram_get_idstr(rb));
> -    range.start = ROUND_DOWN(client_addr, pagesize);
> -    range.len = pagesize;
> -    ret = ioctl(pcfd->fd, UFFDIO_WAKE, &range);
> -    if (ret) {
> -        error_report("%s: Failed to wake: %zx in %s (%s)",
> -                     __func__, (size_t)client_addr, qemu_ram_get_idstr(rb),
> -                     strerror(errno));
> -    }
> -    return ret;
> +    return uffd_wakeup(pcfd->fd, (void *)ROUND_DOWN(client_addr, pagesize),
> +                       pagesize);
>  }

There's a build issue on i386:

../migration/postcopy-ram.c: In function ‘postcopy_wake_shared’:
../migration/postcopy-ram.c:750:34: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
  750 |     return uffd_wakeup(pcfd->fd, (void *)ROUND_DOWN(client_addr, pagesize),
      |                                  ^

The plan is to squash below fix:

=========8<===========
diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
index 03a63ef5cd..83f6160a36 100644
--- a/migration/postcopy-ram.c
+++ b/migration/postcopy-ram.c
-@@ -747,7 +747,8 @@ int postcopy_wake_shared(struct PostCopyFD *pcfd,
 {
     size_t pagesize = qemu_ram_pagesize(rb);
     trace_postcopy_wake_shared(client_addr, qemu_ram_get_idstr(rb));
-    return uffd_wakeup(pcfd->fd, (void *)ROUND_DOWN(client_addr, pagesize),
+    return uffd_wakeup(pcfd->fd,
+                       (void *)(uintptr_t)ROUND_DOWN(client_addr, pagesize),
                        pagesize);
 }
=========8<===========

Thanks,

-- 
Peter Xu