x86/mm/pat: Untangle pat_init()

Split it into a BSP and AP version which makes the PAT
initialization path actually readable again.

Signed-off-by: Borislav Petkov <[email protected]>
Reviewed-by: Toshi Kani <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: [email protected]
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Luis R. Rodriguez <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: linux-mm <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

arch/x86/mm/pat.c

@@ -36,6 +36,8 @@
 #undef pr_fmt
 #define pr_fmt(fmt) "" fmt
 
+static bool boot_cpu_done;
+
 static int __read_mostly __pat_enabled = IS_ENABLED(CONFIG_X86_PAT);
 
 static inline void pat_disable(const char *reason)
@@ -194,31 +196,47 @@ void pat_init_cache_modes(void)
 
 #define PAT(x, y) ((u64)PAT_ ## y << ((x)*8))
 
-void pat_init(void)
+static void pat_bsp_init(u64 pat)
 {
- u64 pat;
- bool boot_cpu = !boot_pat_state;
+ if (!cpu_has_pat) {
+ pat_disable("PAT not supported by CPU.");
+ return;
+ }
 
- if (!pat_enabled())
+ rdmsrl(MSR_IA32_CR_PAT, boot_pat_state);
+ if (!boot_pat_state) {
+ pat_disable("PAT MSR is 0, disabled.");
  return;
+ }
 
+ wrmsrl(MSR_IA32_CR_PAT, pat);
+
+ pat_init_cache_modes();
+}
+
+static void pat_ap_init(u64 pat)
+{
  if (!cpu_has_pat) {
- if (!boot_pat_state) {
- 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.
- */
- pr_err("x86/PAT: PAT enabled, but not supported by secondary CPU\n");
- BUG();
- }
+ /*
+ * If this happens we are on a secondary CPU, but switched to
+ * PAT on the boot CPU. We have no way to undo PAT.
+ */
+ panic("x86/PAT: PAT enabled, but not supported by secondary CPU\n");
  }
 
- /* Set PWT to Write-Combining. All other bits stay the same */
+ wrmsrl(MSR_IA32_CR_PAT, pat);
+}
+
+void pat_init(void)
+{
+ u64 pat;
+
+ if (!pat_enabled())
+ return;
+
  /*
+ * Set PWT to Write-Combining. All other bits stay the same:
+ *
  * PTE encoding used in Linux:
  * PAT
  * |PCD
@@ -233,19 +251,12 @@ void pat_init(void)
  pat = PAT(0, WB) | PAT(1, WC) | PAT(2, UC_MINUS) | PAT(3, UC) |
  PAT(4, WB) | PAT(5, WC) | PAT(6, UC_MINUS) | PAT(7, UC);
 
- /* 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;
- }
+ if (!boot_cpu_done) {
+ pat_bsp_init(pat);
+ boot_cpu_done = true;
+ } else {
+ pat_ap_init(pat);
  }
-
- wrmsrl(MSR_IA32_CR_PAT, pat);
-
- if (boot_cpu)
- pat_init_cache_modes();
 }
 
 #undef PAT