Re: [Qemu-devel] [PATCH RFC 1/2] memory: make MemoryRegion alias migratable

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Igor Mammedov (imammedo@redhat.com) wrote:
> use qemu_ram_alloc_from_ptr() to create aliased RAMBlock
> to the part of original memory region.
> 
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> ---
>  exec.c   | 7 ++++---
>  memory.c | 5 +++++
>  2 files changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/exec.c b/exec.c
> index 3e78de3b8f..daef0cd54f 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2313,7 +2313,7 @@ static void ram_block_add(RAMBlock *new_block, Error **errp, bool shared)
>                                          new_block->used_length,
>                                          DIRTY_CLIENTS_ALL);
>  
> -    if (new_block->host) {
> +    if (new_block->host && !new_block->mr->alias) {
>          qemu_ram_setup_dump(new_block->host, new_block->max_length);
>          qemu_madvise(new_block->host, new_block->max_length, QEMU_MADV_HUGEPAGE);
>          /* MADV_DONTFORK is also needed by KVM in absence of synchronous MMU */
> @@ -2671,7 +2671,8 @@ RAMBlock *qemu_ram_block_from_host(void *ptr, bool round_offset,
>  
>      rcu_read_lock();
>      block = atomic_rcu_read(&ram_list.mru_block);
> -    if (block && block->host && host - block->host < block->max_length) {
> +    if (block && !block->mr->alias && block->host &&
> +        host - block->host < block->max_length) {
>          goto found;
>      }
>  
> @@ -2680,7 +2681,7 @@ RAMBlock *qemu_ram_block_from_host(void *ptr, bool round_offset,
>          if (block->host == NULL) {
>              continue;
>          }
> -        if (host - block->host < block->max_length) {
> +        if (!block->mr->alias && host - block->host < block->max_length) {
>              goto found;
>          }
>      }
> diff --git a/memory.c b/memory.c
> index 5d8c9a9234..d710c17a26 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -1678,6 +1678,11 @@ void memory_region_init_alias(MemoryRegion *mr,
>      memory_region_init(mr, owner, name, size);
>      mr->alias = orig;
>      mr->alias_offset = offset;
> +    if (orig->ram_block && size) {
> +        mr->ram_block = qemu_ram_alloc_from_ptr(size,
> +                                                orig->ram_block->host + offset,
> +                                                mr, &error_fatal);
> +    }
>  }

Doesn't this cause new memory regions to be created in other existing
machines, e.g. x86's mem-smram, or the various PCI vga hacks?

Dave
>  
>  void memory_region_init_rom_nomigrate(MemoryRegion *mr,
> -- 
> 2.18.1
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK