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Re: [PATCH v7 1/2] xen+tools: Report Interrupt Controller Virtualization capabilities on x86


  • To: Jane Malalane <jane.malalane@xxxxxxxxxx>
  • From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • Date: Mon, 14 Mar 2022 11:11:51 +0100
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  • Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Jun Nakajima <jun.nakajima@xxxxxxxxx>, Kevin Tian <kevin.tian@xxxxxxxxx>
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  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On Fri, Mar 11, 2022 at 03:21:06PM +0000, Jane Malalane wrote:
> Add XEN_SYSCTL_PHYSCAP_X86_ASSISTED_XAPIC and
> XEN_SYSCTL_PHYSCAP_X86_ASSISTED_X2APIC to report accelerated xapic
> and x2apic, on x86 hardware.
> No such features are currently implemented on AMD hardware.
> 
> HW assisted xAPIC virtualization will be reported if HW, at the
> minimum, supports virtualize_apic_accesses as this feature alone means
> that an access to the APIC page will cause an APIC-access VM exit. An
> APIC-access VM exit provides a VMM with information about the access
> causing the VM exit, unlike a regular EPT fault, thus simplifying some
> internal handling.
> 
> HW assisted x2APIC virtualization will be reported if HW supports
> virtualize_x2apic_mode and, at least, either apic_reg_virt or
> virtual_intr_delivery. This also means that
> sysctl follows the conditionals in vmx_vlapic_msr_changed().
> 
> For that purpose, also add an arch-specific "capabilities" parameter
> to struct xen_sysctl_physinfo.
> 
> Note that this interface is intended to be compatible with AMD so that
> AVIC support can be introduced in a future patch. Unlike Intel that
> has multiple controls for APIC Virtualization, AMD has one global
> 'AVIC Enable' control bit, so fine-graining of APIC virtualization
> control cannot be done on a common interface.
> 
> Suggested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Signed-off-by: Jane Malalane <jane.malalane@xxxxxxxxxx>

Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Given the request by Kevin, I think you should at least add a comment
in the commit message that exposing the feature is a pre-requisite in
order to make it a per-domain settable, which is the end goal here.

Thanks, Roger.



 


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