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Re: [Xen-devel] [PATCH v2 5/9] x86/vmx: Improvements to LBR MSR handling

> From: Andrew Cooper [mailto:andrew.cooper3@xxxxxxxxxx]
> Sent: Saturday, June 9, 2018 2:49 AM
> The main purpose of this patch is to only ever insert the LBR MSRs into the
> guest load/save list once, as a future patch wants to change the behaviour
> of
> vmx_add_guest_msr().
> The repeated processing of lbr_info and the guests MSR load/save list is
> redundant, and a guest using LBR itself will have to re-enable
> MSR_DEBUGCTL.LBR in its #DB handler, meaning that Xen will repeat this
> redundant processing every time the guest gets a debug exception.
> Rename lbr_fixup_enabled to lbr_flags to be a little more generic, and use
> one
> bit to indicate that the MSRs have been inserted into the load/save list.
> Shorten the existing FIXUP* identifiers to reduce code volume.
> Finally, the enablement of the fixups only need to be calculated once,
> rather
> than inside a doubly nested loop.
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Acked-by: Kevin Tian <kevin.tian@xxxxxxxxx>
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