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Re: [Xen-devel] [PATCH v4 5/7] libxl: support unmapping static shared memory areas during domain destruction

On 12/02/18 15:17, Zhongze Liu wrote:
Hi Julien,


2018-02-12 23:09 GMT+08:00 Julien Grall <julien.grall@xxxxxxx>:

On 12/02/18 14:52, Zhongze Liu wrote:

2018-02-08 0:54 GMT+08:00 Julien Grall <julien.grall@xxxxxxx>:

On 07/02/18 16:27, Zhongze Liu wrote:

It seems that I mistakenly use transaction as a global lock. Now I don't
any reasons not putting the unmap out of the transaction, but this will
the original transaction into two, and I do think that we need some
locking here.

Can you explain why you need specific locking here? What are you trying to
protect? Are you trying to protect against two process doing the unmap?


I don't think you have to worry about the locking here. With the current interface, the regions cannot be modified after the guest has booted. So the addresses will always stay valid.

This code path should never be called concurrently, as a lot of code in libxl, so I think someone else will take care about that for you (I will let Wei confirm here).

In any case, the worst that could happen is the unmap is called twice on the same region. So you would get spurious error message. Not that bad.


Julien Grall

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