[PATCH] x86: Add a turbo mode sysctl

[Andy Lutomirski <luto@kernel.org>]

Sadly, hardware turbo mode buttons are few and far between in these
degenerate times.  Add a software control at /proc/sys/turbo_mode.

Unfortunately, Linux graphical environments have become very
heavy-weight and are essentially unusable on non-Turbo systems.  The
VT console works very well, though.

Due to KVM limitations, turbo mode is permanently on in a KVM guest.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 arch/x86/mm/pat.c | 63 +++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 61 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index faec01e7a17d..f703d8b1ed20 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -69,6 +69,8 @@ static int __init pat_debug_setup(char *str)
 }
 __setup("debugpat", pat_debug_setup);
 
+static int turbo_mode = 1;
+
 #ifdef CONFIG_X86_PAT
 /*
  * X86 PAT uses page flags arch_1 and uncached together to keep track of
@@ -176,6 +178,62 @@ static enum page_cache_mode pat_get_cache_mode(unsigned pat_val, char *msg)
 
 #undef CM
 
+#define PAT(x, y)	((u64)PAT_ ## y << ((x)*8))
+
+static void update_local_turbo_mode(void *dummy)
+{
+	unsigned long cr0 = read_cr0();
+
+	/*
+	 * KVM doesn't properly handle CD.
+	 *
+	 * XXX: this may interact poorly with CPU hotplug.
+	 */
+
+	if (turbo_mode)
+		write_cr0(cr0 & ~X86_CR0_CD);
+	else
+		write_cr0(cr0 | X86_CR0_CD);
+}
+
+static void update_turbo_mode(void)
+{
+	on_each_cpu(update_local_turbo_mode, NULL, 1);
+
+	if (!turbo_mode)
+		wbinvd();
+}
+
+static int turbo_mode_handler(struct ctl_table *table, int write,
+			      void __user *buffer, size_t *lenp,
+			      loff_t *ppos)
+{
+        int error;
+
+        error = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+        if (error)
+                return error;
+
+        if (write)
+		update_turbo_mode();
+
+        return 0;
+}
+
+static int zero, one = 1;
+static struct ctl_table turbo_mode_table[] = {
+	{
+		.procname	= "turbo_mode",
+		.data		= &turbo_mode,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= turbo_mode_handler,
+		.extra1		= &zero,
+		.extra2		= &one,
+	},
+	{}
+};
+
 /*
  * Update the cache mode to pgprot translation tables according to PAT
  * configuration.
@@ -196,8 +254,6 @@ void pat_init_cache_modes(u64 pat)
 	pr_info("x86/PAT: Configuration [0-7]: %s\n", pat_msg);
 }
 
-#define PAT(x, y)	((u64)PAT_ ## y << ((x)*8))
-
 static void pat_bsp_init(u64 pat)
 {
 	u64 tmp_pat;
@@ -1096,6 +1152,9 @@ static int __init pat_memtype_list_init(void)
 		debugfs_create_file("pat_memtype_list", S_IRUSR,
 				    arch_debugfs_dir, NULL, &memtype_fops);
 	}
+
+	register_sysctl_table(turbo_mode_table);
+
 	return 0;
 }
 
-- 
2.5.5