UBUNTU: SAUCE: kvm: x86: mmu: Apply global mitigations knob to ITLB_MULTIHIT

Problem: The global mitigation knob mitigations=off does not turn off
X86_BUG_ITLB_MULTIHIT mitigation.

Fix: Turn off the mitigation when ITLB_MULTIHIT mitigation mode is
"auto" and mitigations are turned off globally via cmdline
mitigations=off.
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>

CVE-2018-12207

[tyhicks Backport to 4.4
 - Minor context adjustment due to missing kvm_set_mmio_spte_mask()
 - kernel-parameters.txt is up one directory level]
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

Documentation/kernel-parameters.txt

@@ -2295,6 +2295,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 					       l1tf=off [X86]
 					       mds=off [X86]
 					       tsx_async_abort=off [X86]
+					       kvm.nx_huge_pages=off [X86].
+
+				Exceptions:
+					       This does not have any effect on
+					       kvm.nx_huge_pages when
+					       kvm.nx_huge_pages=force.
 
 			auto (default)
 				Mitigate all CPU vulnerabilities, but leave SMT

arch/x86/kvm/mmu.c

@@ -4991,6 +4991,12 @@ static void mmu_destroy_caches(void)
 		kmem_cache_destroy(mmu_page_header_cache);
 }
 
+static bool get_nx_auto_mode(void)
+{
+	/* Return true when CPU has the bug, and mitigations are ON */
+	return boot_cpu_has_bug(X86_BUG_ITLB_MULTIHIT) && !cpu_mitigations_off();
+}
+
 static void __set_nx_huge_pages(bool val)
 {
 	nx_huge_pages = itlb_multihit_kvm_mitigation = val;
@@ -5007,7 +5013,7 @@ static int set_nx_huge_pages(const char *val, const struct kernel_param *kp)
 	else if (sysfs_streq(val, "force"))
 		new_val = 1;
 	else if (sysfs_streq(val, "auto"))
-		new_val = boot_cpu_has_bug(X86_BUG_ITLB_MULTIHIT);
+		new_val = get_nx_auto_mode();
 	else if (strtobool(val, &new_val) < 0)
 		return -EINVAL;
 
@@ -5035,7 +5041,7 @@ static int set_nx_huge_pages(const char *val, const struct kernel_param *kp)
 int kvm_mmu_module_init(void)
 {
 	if (nx_huge_pages == -1)
-		__set_nx_huge_pages(boot_cpu_has_bug(X86_BUG_ITLB_MULTIHIT));
+		__set_nx_huge_pages(get_nx_auto_mode());
 
 	pte_list_desc_cache = kmem_cache_create("pte_list_desc",
 					    sizeof(struct pte_list_desc),