x86_virt_spec_ctrl(u64 guest_spec_ctrl, u64 guest_virt_spec_ctrl, bool setguest)
{
	u64 msrval, guestval, hostval = x86_spec_ctrl_base;
	struct thread_info *ti = current_thread_info();

	/* Is MSR_SPEC_CTRL implemented ? */
	if (static_cpu_has(X86_FEATURE_MSR_SPEC_CTRL)) {
		/*
		 * Restrict guest_spec_ctrl to supported values. Clear the
		 * modifiable bits in the host base value and or the
		 * modifiable bits from the guest value.
		 */
		guestval = hostval & ~x86_spec_ctrl_mask;
		guestval |= guest_spec_ctrl & x86_spec_ctrl_mask;

		/* SSBD controlled in MSR_SPEC_CTRL */
		if (static_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD) ||
		    static_cpu_has(X86_FEATURE_AMD_SSBD))
			hostval |= ssbd_tif_to_spec_ctrl(ti->flags);

		if (hostval != guestval) {
			msrval = setguest ? guestval : hostval;
			wrmsrl(MSR_IA32_SPEC_CTRL, msrval);
		}
	}

	/*
	 * If SSBD is not handled in MSR_SPEC_CTRL on AMD, update
	 * MSR_AMD64_L2_CFG or MSR_VIRT_SPEC_CTRL if supported.
	 */
	if (!static_cpu_has(X86_FEATURE_LS_CFG_SSBD) &&
	    !static_cpu_has(X86_FEATURE_VIRT_SSBD))
		return;

	/*
	 * If the host has SSBD mitigation enabled, force it in the host's
	 * virtual MSR value. If its not permanently enabled, evaluate
	 * current's TIF_SSBD thread flag.
	 */
	if (static_cpu_has(X86_FEATURE_SPEC_STORE_BYPASS_DISABLE))
		hostval = SPEC_CTRL_SSBD;
	else
		hostval = ssbd_tif_to_spec_ctrl(ti->flags);

	/* Sanitize the guest value */
	guestval = guest_virt_spec_ctrl & SPEC_CTRL_SSBD;

	if (hostval != guestval) {
		unsigned long tif;

		tif = setguest ? ssbd_spec_ctrl_to_tif(guestval) :
				 ssbd_spec_ctrl_to_tif(hostval);

		speculative_store_bypass_update(tif);
	}
}

Unknown