Commit-ID: 5e8105950a8b3e03e805299b4d05020ee4eda31a
Gitweb: https://git.kernel.org/tip/5e8105950a8b3e03e805299b4d05020ee4eda31a
Author: Joerg Roedel <jroedel@xxxxxxx>
AuthorDate: Wed, 18 Jul 2018 11:41:15 +0200
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Fri, 20 Jul 2018 01:11:48 +0200
x86/mm/pti: Add Warning when booting on a PCID capable CPU
Warn the user in case the performance can be significantly improved by
switching to a 64-bit kernel.
Suggested-by: Andy Lutomirski <luto@xxxxxxxxxx>
Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Pavel Machek <pavel@xxxxxx>
Cc: "H . Peter Anvin" <hpa@xxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Jiri Kosina <jkosina@xxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: David Laight <David.Laight@xxxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: Eduardo Valentin <eduval@xxxxxxxxxx>
Cc: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: aliguori@xxxxxxxxxx
Cc: daniel.gruss@xxxxxxxxxxxxxx
Cc: hughd@xxxxxxxxxx
Cc: keescook@xxxxxxxxxx
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Waiman Long <llong@xxxxxxxxxx>
Cc: "David H . Gutteridge" <dhgutteridge@xxxxxxxxxxxx>
Cc: joro@xxxxxxxxxx
Link: https://lkml.kernel.org/r/1531906876-13451-39-git-send-email-joro@xxxxxxxxxx
---
arch/x86/mm/pti.c | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)
diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index a536ecc91847..7b1c85759005 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -517,6 +517,28 @@ void __init pti_init(void)
pr_info("enabled\n");
+#ifdef CONFIG_X86_32
+ /*
+ * We check for X86_FEATURE_PCID here. But the init-code will
+ * clear the feature flag on 32 bit because the feature is not
+ * supported on 32 bit anyway. To print the warning we need to
+ * check with cpuid directly again.
+ */
+ if (cpuid_ecx(0x1) && BIT(17)) {
+ /* 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();
/* Undo all global bits from the init pagetables in head_64.S: */
--
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