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Re: [PATCH v10 2/2] x86/xen: Allow per-domain usage of hardware virtualized APIC


  • To: Jane Malalane <jane.malalane@xxxxxxxxxx>
  • From: Anthony PERARD <anthony.perard@xxxxxxxxxx>
  • Date: Fri, 29 Apr 2022 14:27:19 +0100
  • Authentication-results: esa2.hc3370-68.iphmx.com; dkim=none (message not signed) header.i=none
  • Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, "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>, Christian Lindig <christian.lindig@xxxxxxxxxx>, David Scott <dave@xxxxxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
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On Wed, Apr 13, 2022 at 12:21:11PM +0100, Jane Malalane wrote:
> Introduce a new per-domain creation x86 specific flag to
> select whether hardware assisted virtualization should be used for
> x{2}APIC.
> 
> A per-domain option is added to xl in order to select the usage of
> x{2}APIC hardware assisted virtualization, as well as a global
> configuration option.
> 
> Having all APIC interaction exit to Xen for emulation is slow and can
> induce much overhead. Hardware can speed up x{2}APIC by decoding the
> APIC access and providing a VM exit with a more specific exit reason
> than a regular EPT fault or by altogether avoiding a VM exit.
> 
> On the other hand, being able to disable x{2}APIC hardware assisted
> virtualization can be useful for testing and debugging purposes.
> 
> Note:
> 
> - vmx_install_vlapic_mapping doesn't require modifications regardless
> of whether the guest has "Virtualize APIC accesses" enabled or not,
> i.e., setting the APIC_ACCESS_ADDR VMCS field is fine so long as
> virtualize_apic_accesses is supported by the CPU.
> 
> - Both per-domain and global assisted_x{2}apic options are not part of
> the migration stream, unless explicitly set in the respective
> configuration files. Default settings of assisted_x{2}apic done
> internally by the toolstack, based on host capabilities at create
> time, are not migrated.
> 
> Suggested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Signed-off-by: Jane Malalane <jane.malalane@xxxxxxxxxx>
> Reviewed-by: "Roger Pau Monné" <roger.pau@xxxxxxxxxx>

Reviewed-by: Anthony PERARD <anthony.perard@xxxxxxxxxx> # tools

-- 
Anthony PERARD



 


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