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Re: [PATCH] x86/vmx: Fold VMCS logic in vmx_{get,set}_segment_register()
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Fri, 21 Jan 2022 14:53:08 +0100
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Jun Nakajima <jun.nakajima@xxxxxxxxx>, Kevin Tian <kevin.tian@xxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Fri, 21 Jan 2022 13:53:24 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 21.01.2022 12:08, Andrew Cooper wrote:
> Xen's segment enumeration almost matches the VMCS encoding order, while the
> VMCS encoding order has the system segments immediately following the user
> segments for all relevant attributes.
>
> Use a sneaky xor to hide the difference in encoding order to fold the switch
> statements, dropping 10 __vmread() and 10 __vmwrite() calls. Bloat-o-meter
> reports:
>
> add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-433 (-433)
> Function old new delta
> vmx_set_segment_register 804 593 -211
> vmx_get_segment_register 778 556 -222
>
> showing that these wrappers aren't trivial. In addition, 20 BUGs worth of
> metadata are dropped.
>
> No functional change.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
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