RE: [PATCH 2/3] x86/boot: Don't enable EFER.SCE for !CONFIG_PV builds

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

> From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Sent: Monday, April 20, 2020 10:59 PM
> 
> This will cause all SYSCALL/SYSRET instructions to suffer #UD rather than
> following the MSR_{L,C}STAR pointers, allowing us to drop the star_enter()
> panic helper, allowing us to clean up the IST stacks in a subsequent patch.
> 
> Drop the now-dead conditional SYSENTER logic in the middle of
> subarch_percpu_traps_init().
> 
> In addition, vmx_restore_host_msrs() need not restore any host
> state.  (Regarding the asymmetric changes, VT-x automatically restores
> SYSENTER state on vmexit, and SVM restores both SYSCALL/SYSENTER state
> with
> the VMSAVE/VMLOAD instructions.)
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

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