Re: Merging KVM live migration upstream

[Anthony Liguori <anthony@codemonkey.ws>]

Jan Kiszka wrote:
> Avi or Uri,
>
> could you explain the first and third hunk? Why are they needed in
> qemu-kvm, and will we also need something comparable upstream? They do
> not look very beautiful.
>   

This is leftovers from v1 loading.  It used to be that we saved the vga 
buffer independently before slot tracking was as sophisticated in qemu 
as it is today.  We don't restore v1 vga that would contain this section 
though so it's basically dead code.

I'd just remove it personally.

> The second hunk, I guess, should become a kvm hook to
> cpu_physical_memory_get_dirty - or is this too costly for other users of
> this inline function?
>
> And does anyone knows further migration-related hunks that are missing
> upstream (except for the KVM hook in
> cpu_physical_memory_set_dirty_tracking)?
>   

The cpu_save/cpu_load additions.

> Jan
>
> --- qemu/vl.c
> +++ qemu-kvm/vl.c
> @@ -3097,6 +3204,8 @@ static int ram_load_v1(QEMUFile *f, void
>      if (qemu_get_be32(f) != last_ram_offset)
>          return -EINVAL;
>      for(i = 0; i < last_ram_offset; i+= TARGET_PAGE_SIZE) {
> +        if (kvm_enabled() && (i>=0xa0000) && (i<0xc0000)) /* do not access video-addresses */
> +            continue;
>          ret = ram_get_page(f, qemu_get_ram_ptr(i), TARGET_PAGE_SIZE);
>          if (ret)
>              return ret;
> @@ -3183,6 +3292,15 @@ static int ram_save_block(QEMUFile *f)
>      int found = 0;
>
>      while (addr < last_ram_offset) {
> +        if (kvm_enabled() && current_addr == 0) {
> +            int r;
> +            r = kvm_update_dirty_pages_log();
> +            if (r) {
> +                fprintf(stderr, "%s: update dirty pages log failed %d\n", __FUNCTION__, r);
> +                qemu_file_set_error(f);
> +                return 0;
> +            }
> +        }
>          if (cpu_physical_memory_get_dirty(current_addr, MIGRATION_DIRTY_FLAG)) {
>              uint8_t *p;
>
> @@ -3273,6 +3391,8 @@ static int ram_load_dead(QEMUFile *f, vo
>      if (ram_decompress_open(s, f) < 0)
>          return -EINVAL;
>      for(i = 0; i < last_ram_offset; i+= BDRV_HASH_BLOCK_SIZE) {
> +        if (kvm_enabled() && (i>=0xa0000) && (i<0xc0000)) /* do not access video-addresses */
> +            continue;
>          if (ram_decompress_buf(s, buf, 1) < 0) {
>              fprintf(stderr, "Error while reading ram block header\n");
>              goto error;
>
>