Re: [Xen-devel] [PATCH v9 1/5] x86/ioreq server: Release the p2m lock after mmio is handled.

[George Dunlap <dunlapg@xxxxxxxxx>]

On Tue, Mar 21, 2017 at 2:52 AM, Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
> Routine hvmemul_do_io() may need to peek the p2m type of a gfn to
> select the ioreq server. For example, operations on gfns with
> p2m_ioreq_server type will be delivered to a corresponding ioreq
> server, and this requires that the p2m type not be switched back
> to p2m_ram_rw during the emulation process. To avoid this race
> condition, we delay the release of p2m lock in hvm_hap_nested_page_fault()
> until mmio is handled.
>
> Note: previously in hvm_hap_nested_page_fault(), put_gfn() was moved
> before the handling of mmio, due to a deadlock risk between the p2m
> lock and the event lock(in commit 77b8dfe). Later, a per-event channel
> lock was introduced in commit de6acb7, to send events. So we do not
> need to worry about the deadlock issue.
>
> Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Who else's ack does this need?  It seems like this is a general
improvement that can go in without the rest of the series.

 -George

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