[SRU][Xenial][PATCH] UBUNTU: SAUCE: Restore the IBRS host state on VMEXIT

[Colin Ian King]

On 15/01/2019 08:33, Juerg Haefliger wrote:
> BugLink: https://bugs.launchpad.net/bugs/1764956
> 
> IBRS in Ubuntu can be controlled dynamically from userspace. Make sure
> the correct state is restored on VMEXIT.
> 
> Suggested-by: Gavin Guo <gavin.guo at canonical.com>
> Signed-off-by: Juerg Haefliger <juergh at canonical.com>
> ---
>  arch/x86/kernel/cpu/bugs.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> index 15867c20ed1c..63d5b84e680b 100644
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -189,6 +189,10 @@ x86_virt_spec_ctrl(u64 guest_spec_ctrl, u64 guest_virt_spec_ctrl, bool setguest)
>  		if (static_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD))
>  			hostval |= ssbd_tif_to_spec_ctrl(ti->flags);
>  
> +		/* IBRS dynamically controlled in MSR_SPEC_CTRL */
> +		if (ibrs_enabled)
> +			hostval |= SPEC_CTRL_IBRS;
> +
>  		if (hostval != guestval) {
>  			msrval = setguest ? guestval : hostval;
>  			wrmsrl(MSR_IA32_SPEC_CTRL, msrval);
> 

Makes sense.

Acked-by: Colin Ian King <colin.king at canonical.com>