Re: [Xen-devel] [PATCH v6 2/4] x86/ioreq server: Release the p2m lock after mmio is handled.

[Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>]

On 9/9/2016 1:24 PM, Yu Zhang wrote:
> On 9/2/2016 6:47 PM, Yu Zhang 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>
>
> However, shouldn't this go _before_ what is now patch 1?
Yes. This should be the patch 1/4. Thanks! :)

Yu

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