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From: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= <roger.pau@citrix.com>
Subject: Re: [PATCH 5/5] x86/HVM: don't setup an intercept
 handler for IO port 0xcf8 unconditionally
Date: Thu, 14 Jan 2016 12:00:59 +0100
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To: Andrew Cooper <andrew.cooper3@citrix.com>, Jan Beulich <JBeulich@suse.com>
Cc: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>, Paul Durrant <Paul.Durrant@citrix.com>
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El 14/01/16 a les 11.50, Andrew Cooper ha escrit:
> On 14/01/16 09:12, Jan Beulich wrote:
>>>>> On 14.01.16 at 09:35, <roger.pau@citrix.com> wrote:
>>> El 13/01/16 a les 17.48, Paul Durrant ha escrit:
>>>>> -----Original Message-----
>>>>> From: Jan Beulich [mailto:JBeulich@suse.com]
>>>>> Sent: 13 January 2016 16:39
>>>>> To: Paul Durrant; Roger Pau Monne
>>>>> Cc: Andrew Cooper; xen-devel@lists.xenproject.org 
>>>>> Subject: Re: [PATCH 5/5] x86/HVM: don't setup an intercept handler for IO
>>>>> port 0xcf8 unconditionally
>>>>>
>>>>>>>> On 13.01.16 at 13:32, <roger.pau@citrix.com> wrote:
>>>>>> Only intercept accesses to IO port 0xcf8 if there's at least one IOREQ
>>>>>> server, otherwise it makes no sense since the only code that uses the value
>>>>>> stored by hvm_access_cf8 is the IOREQ server.
>>>>> Afaict an ioreq server could also attach subsequently - Paul?
>>>>>
>>>> Indeed, ioreq servers can come and go at any time.
>>> Right, then I will have to prevent hvm_access_cf8 from being added if
>>> the domain is the hardware domain, otherwise it overlaps with the Dom0
>>> passthrough intercept (handle_pvh_io).
>> Yes, that indeed makes sense.
> 
> Even for the hardware domain, cf8 needs trapping and emulating (although
> on a different path).  Being an indirect port pair shared by Xen and
> dom0, dom0 cannot use it directly of its own accord.

Sure, but it has to be handled by handle_pvh_io (which I plan to rename
in due time) and not hvm_access_cf8.

Roger.