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Re: [Xen-devel] [PATCH v3 7/7] xen/dom0: Add a dom0-iommu=none option


  • To: Jan Beulich <JBeulich@xxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Mon, 21 Jan 2019 18:08:59 +0000
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  • Cc: Juergen Gross <jgross@xxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxx>, Julien Grall <julien.grall@xxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>
  • Delivery-date: Mon, 21 Jan 2019 18:10:11 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Openpgp: preference=signencrypt

On 17/01/2019 13:35, Jan Beulich wrote:
>>>> On 16.01.19 at 10:00, <andrew.cooper3@xxxxxxxxxx> wrote:
>> @@ -709,6 +709,12 @@ Controls for the dom0 IOMMU setup.
>>      This option is enabled by default on x86 systems, and invalid on ARM
>>      systems.
>>  
>> +*   The `none` option is intended for development purposes only, and skips
>> +    certain safety checks pertaining to the correct IOMMU configuration for
>> +    dom0 to boot.
> Would you mind inserting "PVH" ahead of "dom0"?

That would result in an inaccurate description of the functionality. 
check_hwdom_reqs() is not specific to PVH guests.

>
>> @@ -156,7 +159,7 @@ int iommu_domain_init(struct domain *d)
>>  
>>  static void __hwdom_init check_hwdom_reqs(struct domain *d)
>>  {
>> -    if ( !paging_mode_translate(d) )
>> +    if ( iommu_hwdom_none || !paging_mode_translate(d) )
>>          return;
> Seeing the __hwdom_init, wouldn't it be better to restrict this
> relaxation to Xen boot time created Dom0?

No, I don't think so.

That would complicate the change (which is already only for use by
developers), and unnecessarily prohibit testing of the late hwdom paths.

~Andrew

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