[v10,10/12] x86, mm, pat: Cleanup init flags in pat_init()

Commit Message

Toshi Kani May 27, 2015, 3:19 p.m. UTC

pat_init() uses two flags, 'boot_cpu' and 'boot_pat_state', for
tracking the boot CPU's initialization status.  'boot_pat_state'
is also overloaded to carry the boot PAT value.

This patch cleans this up by replacing them with a new single
flag, 'boot_cpu_done', to track the boot CPU's initialization
status.  'boot_pat_state' is only used to carry the boot PAT
value as a result.

Suggested-by: Thomas Gleixner <[e-mail]>
Signed-off-by: Toshi Kani <[e-mail]>
---
 arch/x86/mm/pat.c |   42 ++++++++++++++++++++----------------------
 1 file changed, 20 insertions(+), 22 deletions(-)

Comments

Borislav Petkov May 29, 2015, 8:59 a.m. UTC | #1

On Wed, May 27, 2015 at 09:19:02AM -0600, Toshi Kani wrote:
> pat_init() uses two flags, 'boot_cpu' and 'boot_pat_state', for
> tracking the boot CPU's initialization status.  'boot_pat_state'
> is also overloaded to carry the boot PAT value.
> 
> This patch cleans this up by replacing them with a new single
> flag, 'boot_cpu_done', to track the boot CPU's initialization
> status.  'boot_pat_state' is only used to carry the boot PAT
> value as a result.
> 
> Suggested-by: Thomas Gleixner <[e-mail]>
> Signed-off-by: Toshi Kani <[e-mail]>
> ---
>  arch/x86/mm/pat.c |   42 ++++++++++++++++++++----------------------
>  1 file changed, 20 insertions(+), 22 deletions(-)

...

> +		rdmsrl(MSR_IA32_CR_PAT, boot_pat_state);
> +		if (!boot_pat_state) {
> +			pat_disable("PAT read returns always zero, disabled.");
> +			return;
> +		}
> +	} else if (!cpu_has_pat) {
> +		/*
> +		 * If this happens we are on a secondary CPU, but
> +		 * switched to PAT on the boot CPU. We have no way to
> +		 * undo PAT.
> +		 */
> +		pr_err("PAT enabled, but not supported by secondary CPU\n");
> +		BUG();

These could be replaced with a panic().

Patch

diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index 92fc635..7cfd995 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -201,26 +201,31 @@  void pat_init_cache_modes(void)
 void pat_init(void)
 {
 	u64 pat;
-	bool boot_cpu = !boot_pat_state;
 	struct cpuinfo_x86 *c = &boot_cpu_data;
+	static bool boot_cpu_done;
 
 	if (!pat_enabled)
 		return;
 
-	if (!cpu_has_pat) {
-		if (!boot_pat_state) {
+	if (!boot_cpu_done) {
+		if (!cpu_has_pat) {
 			pat_disable("PAT not supported by CPU.");
 			return;
-		} else {
-			/*
-			 * If this happens we are on a secondary CPU, but
-			 * switched to PAT on the boot CPU. We have no way to
-			 * undo PAT.
-			 */
-			printk(KERN_ERR "PAT enabled, "
-			       "but not supported by secondary CPU\n");
-			BUG();
 		}
+
+		rdmsrl(MSR_IA32_CR_PAT, boot_pat_state);
+		if (!boot_pat_state) {
+			pat_disable("PAT read returns always zero, disabled.");
+			return;
+		}
+	} else if (!cpu_has_pat) {
+		/*
+		 * If this happens we are on a secondary CPU, but
+		 * switched to PAT on the boot CPU. We have no way to
+		 * undo PAT.
+		 */
+		pr_err("PAT enabled, but not supported by secondary CPU\n");
+		BUG();
 	}
 
 	if ((c->x86_vendor == X86_VENDOR_INTEL) &&
@@ -279,19 +284,12 @@  void pat_init(void)
 		      PAT(4, WB) | PAT(5, WC) | PAT(6, UC_MINUS) | PAT(7, WT);
 	}
 
-	/* Boot CPU check */
-	if (!boot_pat_state) {
-		rdmsrl(MSR_IA32_CR_PAT, boot_pat_state);
-		if (!boot_pat_state) {
-			pat_disable("PAT read returns always zero, disabled.");
-			return;
-		}
-	}
-
 	wrmsrl(MSR_IA32_CR_PAT, pat);
 
-	if (boot_cpu)
+	if (!boot_cpu_done) {
 		pat_init_cache_modes();
+		boot_cpu_done = true;
+	}
 }
 
 #undef PAT