Re: [Xen-devel] [PATCH v3 3/3] x86/ioreq server: Add HVMOP to map guest ram with p2m_ioreq_server to an ioreq server.

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Yu Zhang [mailto:yu.c.zhang@xxxxxxxxxxxxxxx]
> Sent: 25 April 2016 11:36
> To: xen-devel@xxxxxxxxxxxxx
> Cc: zhiyuan.lv@xxxxxxxxx; Wei Liu; Paul Durrant; Paul Durrant; Keir (Xen.org);
> Jan Beulich; Andrew Cooper; George Dunlap; Jun Nakajima; Kevin Tian; Tim
> (Xen.org)
> Subject: [PATCH v3 3/3] x86/ioreq server: Add HVMOP to map guest ram
> with p2m_ioreq_server to an ioreq server.
> 
> A new HVMOP - HVMOP_map_mem_type_to_ioreq_server, is added to
> let one ioreq server claim/disclaim its responsibility for the
> handling of guest pages with p2m type p2m_ioreq_server. Users
> of this HVMOP can specify which kind of operation is supposed
> to be emulated in a parameter named flags. Currently, this HVMOP
> only support the emulation of write operations. And it can be
> easily extended to support the emulation of read ones if an
> ioreq server has such requirement in the future.
> 
> For now, we only support one ioreq server for this p2m type, so
> once an ioreq server has claimed its ownership, subsequent calls
> of the HVMOP_map_mem_type_to_ioreq_server will fail. Users can also
> disclaim the ownership of guest ram pages with p2m_ioreq_server, by
> triggering this new HVMOP, with ioreq server id set to the current
> owner's and flags parameter set to 0.
> 
> Note both HVMOP_map_mem_type_to_ioreq_server and
> p2m_ioreq_server
> are only supported for HVMs with HAP enabled.
> 
> Also note that only after one ioreq server claims its ownership
> of p2m_ioreq_server, will the p2m type change to p2m_ioreq_server
> be allowed.
> 
> changes in v3:
>   - Only support write emulation in this patch;
>   - Remove the code to handle race condition in hvmemul_do_io(),
>   - No need to reset the p2m type after an ioreq server has disclaimed
>     its ownership of p2m_ioreq_server;
>   - Only allow p2m type change to p2m_ioreq_server after an ioreq
>     server has claimed its ownership of p2m_ioreq_server;

I think this restriction on should be mentioned in hvm_op.h somewhere close to 
where HVMMEM_ioreq_server is defined.

  Paul


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