Re: [Qemu-devel] [RFC v2 3/6] memory: support unmapping of MemoryRegion mapped into HVA parent

[Paolo Bonzini]

On 08/06/2015 17:19, Igor Mammedov wrote:
> +void qemu_ram_unmap_hva(ram_addr_t addr)
> +{
> +    RAMBlock *block = find_ram_block(addr);
> +
> +    assert(block);
> +    mmap(block->host, block->used_length, PROT_NONE,
> +         MAP_FIXED | MAP_NORESERVE | MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
> +}
> +

Hmm, this is not good. :(  The area at block->host can be in use, for
example via memory_region_ref/memory_region_unref.  This can happen a
bit after the memory_region_del_subregion.  So you can SEGV if you
simply make a synchronous update.  I'm not sure if there is a solution
(but thanks for splitting the patches in a way that made the problem
clear!).

Paolo