[RFC 06/13] x86/mm: Disable PCID on 32-bit kernels

[Andy Lutomirski]

32-bit kernels on new hardware will see PCID in CPUID, but PCID can
only be used in 64-bit mode.  Rather than making all PCID code
conditional, just disable the feature on 32-bit builds.

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
---
 arch/x86/include/asm/disabled-features.h | 4 +++-
 arch/x86/kernel/cpu/bugs.c               | 6 ++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/disabled-features.h b/arch/x86/include/asm/disabled-features.h
index f226df064660..8b17c2ad1048 100644
--- a/arch/x86/include/asm/disabled-features.h
+++ b/arch/x86/include/asm/disabled-features.h
@@ -21,11 +21,13 @@
 # define DISABLE_K6_MTRR	(1<<(X86_FEATURE_K6_MTRR & 31))
 # define DISABLE_CYRIX_ARR	(1<<(X86_FEATURE_CYRIX_ARR & 31))
 # define DISABLE_CENTAUR_MCR	(1<<(X86_FEATURE_CENTAUR_MCR & 31))
+# define DISABLE_PCID		0
 #else
 # define DISABLE_VME		0
 # define DISABLE_K6_MTRR	0
 # define DISABLE_CYRIX_ARR	0
 # define DISABLE_CENTAUR_MCR	0
+# define DISABLE_PCID		(1<<(X86_FEATURE_PCID & 31))
 #endif /* CONFIG_X86_64 */
 
 /*
@@ -35,7 +37,7 @@
 #define DISABLED_MASK1	0
 #define DISABLED_MASK2	0
 #define DISABLED_MASK3	(DISABLE_CYRIX_ARR|DISABLE_CENTAUR_MCR|DISABLE_K6_MTRR)
-#define DISABLED_MASK4	0
+#define DISABLED_MASK4	(DISABLE_PCID)
 #define DISABLED_MASK5	0
 #define DISABLED_MASK6	0
 #define DISABLED_MASK7	0
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index bd17db15a2c1..741d107e5376 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -19,6 +19,12 @@
 
 void __init check_bugs(void)
 {
+	/*
+	 * Regardless of whether PCID is enumerated, it can't be used in
+	 * 32-bit mode.
+	 */
+	setup_clear_cpu_cap(X86_FEATURE_PCID);
+
 	identify_boot_cpu();
 #ifndef CONFIG_SMP
 	pr_info("CPU: ");
-- 
2.5.0