Re: [Xen-devel] [PATCH v12 5/6] x86/ioreq server: Asynchronously reset outstanding p2m_ioreq_server entries.

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Yu Zhang [mailto:yu.c.zhang@xxxxxxxxxxxxxxx]
> Sent: Thursday, April 6, 2017 11:54 PM
> 
> After an ioreq server has unmapped, the remaining p2m_ioreq_server
> entries need to be reset back to p2m_ram_rw. This patch does this
> asynchronously with the current p2m_change_entry_type_global()
> interface.
> 
> New field entry_count is introduced in struct p2m_domain, to record
> the number of p2m_ioreq_server p2m page table entries. One nature of
> these entries is that they only point to 4K sized page frames, because
> all p2m_ioreq_server entries are originated from p2m_ram_rw ones in
> p2m_change_type_one(). We do not need to worry about the counting for
> 2M/1G sized pages.
> 
> This patch disallows mapping of an ioreq server, when there's still
> p2m_ioreq_server entry left, in case another mapping occurs right after
> the current one being unmapped, releases its lock, with p2m table not
> synced yet.
> 
> This patch also disallows live migration, when there's remaining
> p2m_ioreq_server entry in p2m table. The core reason is our current
> implementation of p2m_change_entry_type_global() lacks information
> to resync p2m_ioreq_server entries correctly if global_logdirty is
> on.
> 
> Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
> Reviewed-by: Paul Durrant <paul.durrant@xxxxxxxxxx>

Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>

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