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Re: [PATCH v5 07/11] xen/domctl: Introduce XEN_DOMCTL_CDF_vpci flag

  • To: Stefano Stabellini <sstabellini@xxxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Wed, 13 Oct 2021 08:18:48 +0200
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  • Cc: Rahul Singh <rahul.singh@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, bertrand.marquis@xxxxxxx, Andre.Przywara@xxxxxxx, Christian Lindig <christian.lindig@xxxxxxxxxx>, David Scott <dave@xxxxxxxxxx>, Ian Jackson <iwj@xxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • Delivery-date: Wed, 13 Oct 2021 06:19:03 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 12.10.2021 23:48, Stefano Stabellini wrote:
> On Mon, 11 Oct 2021, Roger Pau Monné wrote:
>> On Wed, Oct 06, 2021 at 06:40:33PM +0100, Rahul Singh wrote:
>>> Introduce XEN_DOMCTL_CDF_vpci flag to enable VPCI support in XEN.
>>> Reject the use of this new flag for x86 as VPCI is not supported for
>>> DOMU guests for x86.
>> I don't like this approach, XEN_DOMCTL_CDF_vpci should be set for x86
>> PVH dom0, like we do for any other CDF flags when Xen builds dom0.
>> Things like PVH vs PV get translated into CDF flags by create_dom0,
>> and processed normally by the sanitise_domain_config logic, vPCI
>> should be handled that way.
>> Do you think you could see about fixing this?
> Andrew suggested to use XEN_SYSCTL_PHYSCAP_vpci to check whether we can
> set XEN_DOMCTL_CDF_vpci in libxl and it looks like we have consensus on
> this approach. [1][2]
> So it makes sense that XEN_DOMCTL_CDF_vpci is only set when
> XEN_SYSCTL_PHYSCAP_vpci is also set, i.e. XEN_SYSCTL_PHYSCAP_vpci ==
> From [2], XEN_SYSCTL_PHYSCAP_vpci is not going to be set on x86, so then
> XEN_DOMCTL_CDF_vpci should also be left unset?
> If you think XEN_DOMCTL_CDF_vpci should be set for x86 PVH Dom0, then
> XEN_SYSCTL_PHYSCAP_vpci should also be set for x86 PVH Dom0.

Except that XEN_SYSCTL_PHYSCAP_vpci is not a domain specific attribute,
but a host-wide one.




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