[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] per-domain passthrough/iommu options


  • To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
  • From: Jan Beulich <JBeulich@xxxxxxxx>
  • Date: Mon, 29 Jul 2019 11:10:36 +0000
  • Accept-language: en-US
  • Arc-authentication-results: i=1; mx.microsoft.com 1;spf=pass smtp.mailfrom=suse.com;dmarc=pass action=none header.from=suse.com;dkim=pass header.d=suse.com;arc=none
  • Arc-message-signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector9901; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=3RC4KPMe5XUhGLf4d970eHdNGoccNMT2Z65SlpLYSZ0=; b=nVjr8YpNGPxqP9vipkDTSOIDJUULccjkTcmFNON/SVliCMTq/ldhppaF+Ja4Niw3PzuDQkH4hDuqEEqiWn7y1NS4m8k0FuF7s6593Sg5LGUfZxGrTfPmymu2oI2c25JwY723ZTIxxz5/7QTV9TQ/UAzOdDY6VRf1MHqmRDcCWivUKX5zRtHFOyOYfWueGmGTUx7Fe6e4HajxMwoWf2ZdQvspaP+1lmWQI6DHLTCsxElCyLkCwHBJmKni1ogxcWdNYPMOhLUg5gVb15aLUeZ4Xhv1vvaVal5eBB1HJs/vCm/pBPw5Kzd4/fK4+FZdJyEX8dKvNmN7+ITpUXEHYpBFXQ==
  • Arc-seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=OFPsyniqf/YgHWqkLvG5fwOrG4wyrWhMcLKtqaaFPjZmyKI03DYNX0IM5RBuF3MfMJ/IGGN2t7Cniucr8Z8Fp2MXuQg2bCiFWiFqGnsqHve0ygpIbnsJyD/g3WqROoZ0fe/V2ggCLYmTdT8y2l8fRsd+EQKSVw0DhJ1eJ0Zqyo84qWJcXjiPU/vtfW/rcuAAMZXL6b+IxOEfHWF9hlNzuI2TAYVhFG6aW3kvPrMugwNhmGg2ppQI+dEqHdIJ9GCU5JsyRQjUXX8RyX6YxpSpQFW6LBTVVUVOBIcTOpKi4VeQvvlvaQToTsHUMuE0sn9zqe5HEwGkf/KrAScj1CU5dg==
  • Authentication-results: spf=none (sender IP is ) smtp.mailfrom=JBeulich@xxxxxxxx;
  • Cc: "xen-devel \(xen-devel@xxxxxxxxxxxxxxxxxxxx\)" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Mon, 29 Jul 2019 11:31:13 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Thread-index: AdVDqy2gdS3slVvQRuCN/iB10JmJ2gABnjsAAAD6vMAAAUXLgAAASpcAAADXF4AAAKXGUACPHNGA
  • Thread-topic: [Xen-devel] per-domain passthrough/iommu options

On 26.07.2019 16:54, Paul Durrant wrote:
>> -----Original Message-----
>> From: Jan Beulich <JBeulich@xxxxxxxx>
>> Sent: 26 July 2019 15:34
>> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
>> Cc: xen-devel (xen-devel@xxxxxxxxxxxxxxxxxxxx) 
>> <xen-devel@xxxxxxxxxxxxxxxxxxxx>
>> Subject: Re: [Xen-devel] per-domain passthrough/iommu options
>>
>> On 26.07.2019 16:26, Paul Durrant wrote:
>>>> From: Jan Beulich <JBeulich@xxxxxxxx>
>>>> Sent: 26 July 2019 15:02
>>>>
>>>> On 26.07.2019 15:39, Paul Durrant wrote:
>>>>> ? I don't think 'private-pt' or 'separate-pt' really capture the fact 
>>>>> that the page tables match
>> the
>>>> P2M. They could just as easily be taken to mean that they are populated 
>>>> using some other policy.
>>>>
>>>> But haven't we recently seen that this fully lock-step population
>>>> of page tables isn't always correct (or at least desirable)? I
>>>> vaguely recall other comments to that effect too, from long ago.
>>>> I'd specifically want to avoid encoding into the interface here
>>>> that the two are exact mirrors of one another, now and forever.
>>>
>>> How do you think we should express it. I agree that it's a bit awkward 
>>> because of the difference
>> between HVM and PV domains, but all we can do there really is document it I 
>> think, so perhaps the
>> manpage could have something like:
>>
>> Sounds reasonable - it at least avoids making the behavior too
>> much spelled out with regard to the similarity of mappings between
>> IOMMU page tables and P2M. There's one issue though:
>>
>>> 'off'
>>>
>>> IOMMU mappings are disabled for the domain and so hardware may not be 
>>> passed through.
>>>
>>> 'sync-pt'
>>>
>>> For a PV domain, all writable pages assigned to the domain are identity 
>>> mapped by MFN in the IOMMU
>> page tables. Thus a device driver running in the domain may program 
>> passthrough hardware for DMA using
>> MFN values (i.e. host/machine frame numbers) looked up in its P2M.
>>> For an HVM domain, all non-foreign RAM pages present in the P2M will be 
>>> identity mapped by GFN
>>
>> Why "identity mapped" here? It's a GFN -> MFN mappingm, isn't it?
> 
> Yes... it's hard to express. What I want to say, of course, is that device 
> drivers can use GFNs. Can you think of any other form of words that might be 
> better?

Just omit "identity" in the HVM related sentence?

Jan
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel

 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.