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Re: [Qemu-devel] [PATCH 04/15] memory: MemoryRegion topology must be sta


From: Avi Kivity
Subject: Re: [Qemu-devel] [PATCH 04/15] memory: MemoryRegion topology must be stable when updating
Date: Wed, 08 Aug 2012 12:13:26 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120717 Thunderbird/14.0

On 08/08/2012 09:25 AM, Liu Ping Fan wrote:
> From: Liu Ping Fan <address@hidden>
> 
> Using mem_map_lock to protect among updaters. So we can get the intact
> snapshot of mem topology -- FlatView & radix-tree.
> 
> Signed-off-by: Liu Ping Fan <address@hidden>
> ---
>  exec.c   |    3 +++
>  memory.c |   22 ++++++++++++++++++++++
>  memory.h |    2 ++
>  3 files changed, 27 insertions(+), 0 deletions(-)
> 
> diff --git a/exec.c b/exec.c
> index 8244d54..0e29ef9 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -210,6 +210,8 @@ static unsigned phys_map_nodes_nb, 
> phys_map_nodes_nb_alloc;
>     The bottom level has pointers to MemoryRegionSections.  */
>  static PhysPageEntry phys_map = { .ptr = PHYS_MAP_NODE_NIL, .is_leaf = 0 };
>  
> +QemuMutex mem_map_lock;
> +
>  static void io_mem_init(void);
>  static void memory_map_init(void);
>  
> @@ -637,6 +639,7 @@ void cpu_exec_init_all(void)
>  #if !defined(CONFIG_USER_ONLY)
>      memory_map_init();
>      io_mem_init();
> +    qemu_mutex_init(&mem_map_lock);
>  #endif
>  }
>  
> diff --git a/memory.c b/memory.c
> index aab4a31..5986532 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -761,7 +761,9 @@ void memory_region_transaction_commit(void)
>      assert(memory_region_transaction_depth);
>      --memory_region_transaction_depth;
>      if (!memory_region_transaction_depth && memory_region_update_pending) {
> +        qemu_mutex_lock(&mem_map_lock);
>          memory_region_update_topology(NULL);
> +        qemu_mutex_unlock(&mem_map_lock);
>      }
>  }

Seems to me that nothing in memory.c can susceptible to races.  It must
already be called under the big qemu lock, and with the exception of
mutators (memory_region_set_*), changes aren't directly visible.

I think it's sufficient to take the mem_map_lock at the beginning of
core_begin() and drop it at the end of core_commit().  That means all
updates of volatile state, phys_map, are protected.



-- 
error compiling committee.c: too many arguments to function



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