Re: [Xen-devel] [PATCH 6/6] x86/VT-x: Fix 64bit HVM guests on Harpertown cores

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Andrew Cooper [mailto:andrew.cooper3@xxxxxxxxxx]
> Sent: Friday, December 28, 2018 8:40 PM
> 
> c/s fd32dcfe4c "x86/vmx: Don't leak EFER.NXE into guest context" had an
> unintended consequence on Harpertown cores which, as it turns out, don't
> load MSR_EFER fully from the MSR Load List - on reentry to the guest,
> EFER.SCE is clear irrespective of the value in load list.
> 
> This, being catastrophic to 64bit guests, is far worse than the EFER.NXE
> leakage which was trying to be fixed.
> 
> Introduce cpu_bug_msr_ll_efer_sce to encapsulate this partial revert.
> Avoid adding MSR_EFER to the Load Lists on impacted hardware, and
> reintroduce the logic to use the guests EFER.SCE setting.
> 
> In the common case of running 64bit HVM guests, these extra adjustments
> to EFER should only be hit during guest boot.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

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