Add zen_workaround to our repo

It previously lived at https://gist.github.com/glandium/01d54cefdb70561b5f6675e08f2990f2

Resolves #3690

.gitignore

@@ -35,3 +35,10 @@ share/
 libbrotli*
 extra_version_string.h
 git_revision.h
+zen-pmu-workaround/.*
+zen-pmu-workaround/*.ko
+zen-pmu-workaround/*.o
+zen-pmu-workaround/*.mod
+zen-pmu-workaround/*.mod.c
+zen-pmu-workaround/Module.symvers
+zen-pmu-workaround/modules.order

third-party/zen-pmu-workaround/Makefile

@@ -0,0 +1,7 @@
+obj-m = zen_workaround.o
+
+all:
+	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
+
+clean:
+	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

third-party/zen-pmu-workaround/README

@@ -0,0 +1,2 @@
+Mike Hommey's Zen workaround kernel module.
+There is no upstream, but we put it in third-party because it's technically a derived work of the Linux kernel.

third-party/zen-pmu-workaround/zen_workaround.c

@@ -0,0 +1,114 @@
+#include <linux/module.h>
+#include <linux/tracepoint.h>
+#include <linux/suspend.h>
+
+#define MODULE_NAME "zen_workaround"
+
+#define SPECLOCKMAP_DISABLE BIT_64(54)
+
+u64 set_speclockmap_disable(u64 msr) {
+	return msr | SPECLOCKMAP_DISABLE;
+}
+
+u64 unset_speclockmap_disable(u64 msr) {
+	return msr & ~SPECLOCKMAP_DISABLE;
+}
+
+typedef u64 (*edit_msr_func_t)(u64);
+
+static void edit_ls_cfg_on_cpu(void *info)
+{
+	int cpu = get_cpu();
+	u64 value = 0;
+
+	if (!rdmsrl_safe(MSR_AMD64_LS_CFG, &value)) {
+		edit_msr_func_t edit_msr = (edit_msr_func_t) info;
+		u64 new_value = edit_msr(value);
+		if (!wrmsrl_safe(MSR_AMD64_LS_CFG, new_value)) {
+			pr_info("MSR_AMD64_LS_CFG for cpu %d was 0x%llx, setting to 0x%llx\n",
+			        cpu, value, new_value);
+		} else {
+			pr_err("MSR_AMD64_LS_CFG for cpu %d was 0x%llx, setting to 0x%llx failed\n",
+			       cpu, value, new_value);
+		}
+	}
+
+	put_cpu();
+}
+
+static void do_zen_workaround(edit_msr_func_t edit_msr)
+{
+	smp_call_function(edit_ls_cfg_on_cpu, edit_msr, 1);
+	edit_ls_cfg_on_cpu(edit_msr);
+}
+
+void on_write_msr(void *data, unsigned int msr, u64 val, int failed)
+{
+	if (msr == MSR_AMD64_LS_CFG && !(val & SPECLOCKMAP_DISABLE)) {
+		native_wrmsrl(MSR_AMD64_LS_CFG, set_speclockmap_disable(val));
+	}
+}
+
+static int install_probe(void)
+{
+	return !boot_cpu_has(X86_FEATURE_AMD_SSBD) && !boot_cpu_has(X86_FEATURE_VIRT_SSBD);
+}
+
+static int enable_zen_workaround(void)
+{
+	if (install_probe()) {
+		int ret = tracepoint_probe_register(&__tracepoint_write_msr, on_write_msr, NULL);
+		if (ret) {
+			pr_err("Registering tracepoint probe failed\n");
+			return ret;
+		}
+	}
+	do_zen_workaround(set_speclockmap_disable);
+	return 0;
+}
+
+static int pm_notification(struct notifier_block *this, unsigned long event, void *ptr)
+{
+	switch (event) {
+		case PM_POST_SUSPEND:
+		case PM_POST_HIBERNATION:
+		case PM_POST_RESTORE:
+			enable_zen_workaround();
+			break;
+		case PM_HIBERNATION_PREPARE:
+		case PM_SUSPEND_PREPARE:
+			if (install_probe()) {
+				tracepoint_probe_unregister(&__tracepoint_write_msr, on_write_msr, NULL);
+			}
+			break;
+	}
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block pm_notifier = {
+	.notifier_call = pm_notification,
+};
+
+static int __init zen_workaround_init(void)
+{
+	if (!boot_cpu_has(X86_FEATURE_ZEN)) {
+		pr_err("Cannot use the Zen workaround on a non-Zen CPU\n");
+		return -EINVAL;
+	}
+	enable_zen_workaround();
+	register_pm_notifier(&pm_notifier);
+	return 0;
+}
+module_init(zen_workaround_init);
+
+static void __exit zen_workaround_exit(void)
+{
+	unregister_pm_notifier(&pm_notifier);
+	if (install_probe()) {
+		tracepoint_probe_unregister(&__tracepoint_write_msr, on_write_msr, NULL);
+	}
+	do_zen_workaround(unset_speclockmap_disable);
+}
+module_exit(zen_workaround_exit);
+
+MODULE_LICENSE("GPL");