[PATCH 34/35] x86/mm/pti: Add Warning when booting on a PCID capable CPU

[Joerg Roedel]

From: Joerg Roedel <jroe...@suse.de>

Warn the user in case the performance can be significantly
improved by switching to a 64-bit kernel.

Suggested-by: Andy Lutomirski <l...@kernel.org>
Signed-off-by: Joerg Roedel <jroe...@suse.de>
---
 arch/x86/mm/pti.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index 3ffd923..8f5aa0d 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -385,6 +385,22 @@ void __init pti_init(void)
 
        pr_info("enabled\n");
 
+#ifdef CONFIG_X86_32
+       if (boot_cpu_has(X86_FEATURE_PCID)) {
+               /* Use printk to work around pr_fmt() */
+               printk(KERN_WARNING "\n");
+               printk(KERN_WARNING 
"************************************************************\n");
+               printk(KERN_WARNING "** WARNING! WARNING! WARNING! WARNING! 
WARNING! WARNING!  **\n");
+               printk(KERN_WARNING "**                                         
               **\n");
+               printk(KERN_WARNING "** You are using 32-bit PTI on a 64-bit 
PCID-capable CPU. **\n");
+               printk(KERN_WARNING "** Your performance will increase 
dramatically if you     **\n");
+               printk(KERN_WARNING "** switch to a 64-bit kernel!              
               **\n");
+               printk(KERN_WARNING "**                                         
               **\n");
+               printk(KERN_WARNING "** WARNING! WARNING! WARNING! WARNING! 
WARNING! WARNING!  **\n");
+               printk(KERN_WARNING 
"************************************************************\n");
+       }
+#endif
+
        pti_clone_user_shared();
        pti_clone_entry_text();
        pti_setup_espfix64();
-- 
2.7.4