Re: [Xen-devel] [PATCH V4] x86/ioreq_server: Make p2m_finish_type_change actually work

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On Fri, May 12, 2017 at 3:42 AM, Xiong Zhang <xiong.y.zhang@xxxxxxxxx> wrote:
> Commit 6d774a951696 ("x86/ioreq server: synchronously reset outstanding
> p2m_ioreq_server entries when an ioreq server unmaps") introduced
> p2m_finish_type_change(), which was meant to synchronously finish a
> previously initiated type change over a gpfn range.  It did this by
> calling get_entry(), checking if it was the appropriate type, and then
> calling set_entry().
>
> Unfortunately, a previous commit (1679e0df3df6 "x86/ioreq server:
> asynchronously reset outstanding p2m_ioreq_server entries") modified
> get_entry() to always return the new type after the type change, meaning
> that p2m_finish_type_change() never changed any entries.  Which means
> when an ioreq server was detached and then re-attached (as happens in
> XenGT on reboot) the re-attach failed.
>
> Fix this by using the existing p2m-specific recalculation logic instead
> of doing a read-check-write loop.
>
> Fix: 'commit 6d774a951696 ("x86/ioreq server: synchronously reset
>       outstanding p2m_ioreq_server entries when an ioreq server unmaps")'
>
> Signed-off-by: Xiong Zhang <xiong.y.zhang@xxxxxxxxx>
> Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
> Reviewed-by: George Dunlap <george.dunlap@xxxxxxxxx>
> ---
> v1: Add ioreq_pre_recalc query flag to get the old p2m_type.(Jan)
> v2: Add p2m->recalc() hook to change gfn p2m_type. (George)
> v3: Make commit message clearer. (George)
>     Keep the name of p2m-specific recal function unchanged. (Jan)
> v4: Move version info below S-o-B and handle return value of
>     p2m->recalc. (Jan)

Sorry to be picky, but the handling of the return value introduces
another way the patch could be incorrect, so you should have dropped
my R-b.

I'll respond to v5.

 -George

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