On Thu, Aug 09, 2012 at 03:28:44PM +0800, liu ping fan wrote:
> On Wed, Aug 8, 2012 at 5:13 PM, Avi Kivity <avi@xxxxxxxxxx> wrote:
> > On 08/08/2012 09:25 AM, Liu Ping Fan wrote:
> >> From: Liu Ping Fan <pingfank@xxxxxxxxxxxxxxxxxx>
> >>
> >> 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 <pingfank@xxxxxxxxxxxxxxxxxx>
> >> ---
> >> 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.
> >
> Yes, what I want to do is "prepare unplug out of protection of global
> lock". When io-dispatch and mmio-dispatch are all out of big lock, we
> will run into the following scene:
> In vcpu context A, qdev_unplug_complete()-> delete subregion;
> In context B, write pci bar --> pci mapping update -> add subregion
Per device lock should protect that.
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