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Date: Mon, 29 Sep 2014 14:57:12 +0200
From: Alexander Graf <agraf@suse.de>
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Subject: Re: [Qemu-devel] [PATCH 1/1] xen-hvm.c: Add support for Xen access
	to vmport
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To: Paolo Bonzini <pbonzini@redhat.com>, Don Slutz <dslutz@verizon.com>, qemu-devel@nongnu.org
Cc: xen-devel@lists.xensource.com, Marcel Apfelbaum <marcel.a@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>, Markus Armbruster <armbru@redhat.com>, Anthony Liguori <aliguori@amazon.com>, =?windows-1252?Q?Andreas_F=E4rber?= <afaerber@suse.de>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>



On 29.09.14 14:21, Paolo Bonzini wrote:
> Il 29/09/2014 13:53, Alexander Graf ha scritto:
>>
>>   cpu_handle_ioreq()
>>   {
>>     ...
>>
>>     if (req->type == IOPORT_REGISTERS_SYNCHRONIZED) {
>>         cpu->xen_vcpu_dirty = true;
>>         synchronize_xen_to_env(xenptr, cpu);
>>     }
>>
>>     handle_ioreq();
>>
>>     if (req->type == IOPORT_REGISTERS_SYNCHRONIZED) {
>>         cpu->xen_vcpu_dirty = false;
>>         synchronize_env_to_xen(xenptr, cpu);
>>     }
>>
>>     ...
>>   }
>>
>>   void xen_cpu_synchronize_state(CPUState *cpu)
>>   {
>>     assert(cpu->xen_vcpu_dirty);
>>   }
>>
>> Then no changes to the vmport code would be necessary and this problems
>> where some code path wants to do direct access to registers
>> automatically tells us that things are broken.
> 
> Yeah, that would be possible.  You do not even need synchronize_state,
> it seems to me that it introduces more complication for little gain.

Well, it makes all accels behave the same and keep information always at
a single entity (the env struct). I don't think the vmport code should
have knowledge of a xen env struct.


Alex