Re: [PATCH V1 09/32] savevm: prevent cprsave if memory is volatile

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

* Steve Sistare (steven.sistare@oracle.com) wrote:
> cprsave and cprload require that guest ram be backed by an externally
> visible shared file.  Check that in cprsave.
> 
> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
> ---
>  exec.c                | 32 ++++++++++++++++++++++++++++++++
>  include/exec/memory.h |  2 ++
>  migration/savevm.c    |  4 ++++
>  3 files changed, 38 insertions(+)
> 
> diff --git a/exec.c b/exec.c
> index 6f381f9..02160e0 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2726,6 +2726,38 @@ ram_addr_t qemu_ram_addr_from_host(void *ptr)
>      return block->offset + offset;
>  }
>  
> +/*
> + * Return true if any memory regions are writable and not backed by shared
> + * memory.  Exclude x86 option rom shadow "pc.rom" by name, even though it is
> + * writable.

Tell me about 'pc.rom' - this is a very odd hack.
Again note the trick done by the existing migration capability
x-ignore-shared ; it doesn't special case, it just doesn't migrate
the 'shared' blocks.

Dave


> + */
> +bool qemu_ram_volatile(Error **errp)
> +{
> +    RAMBlock *block;
> +    MemoryRegion *mr;
> +    bool ret = false;
> +
> +    rcu_read_lock();
> +    QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
> +        mr = block->mr;
> +        if (mr &&
> +            memory_region_is_ram(mr) &&
> +            !memory_region_is_ram_device(mr) &&
> +            !memory_region_is_rom(mr) &&
> +            (!mr->name || strcmp(mr->name, "pc.rom")) &&
> +            (block->fd == -1 || !qemu_ram_is_shared(block))) {
> +
> +            error_setg(errp, "Memory region %s is volatile",
> +                       memory_region_name(mr));
> +            ret = true;
> +            break;
> +        }
> +    }
> +
> +    rcu_read_unlock();
> +    return ret;
> +}
> +
>  /* Generate a debug exception if a watchpoint has been hit.  */
>  void cpu_check_watchpoint(CPUState *cpu, vaddr addr, vaddr len,
>                            MemTxAttrs attrs, int flags, uintptr_t ra)
> diff --git a/include/exec/memory.h b/include/exec/memory.h
> index 307e527..6aafbb0 100644
> --- a/include/exec/memory.h
> +++ b/include/exec/memory.h
> @@ -2519,6 +2519,8 @@ bool ram_block_discard_is_disabled(void);
>   */
>  bool ram_block_discard_is_required(void);
>  
> +bool qemu_ram_volatile(Error **errp);
> +
>  #endif
>  
>  #endif
> diff --git a/migration/savevm.c b/migration/savevm.c
> index 1509173..f101039 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -2713,6 +2713,10 @@ void save_cpr_snapshot(const char *file, const char *mode, Error **errp)
>          return;
>      }
>  
> +    if (op == VMS_REBOOT && qemu_ram_volatile(errp)) {
> +        return;
> +    }
> +
>      f = qf_file_open(file, O_CREAT | O_WRONLY | O_TRUNC, 0600, errp);
>      if (!f) {
>          return;
> -- 
> 1.8.3.1
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK