Commit 5e810595 authored Jul 18, 2018 by Joerg Roedel Committed by Thomas Gleixner Jul 20, 2018

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@kernel.org>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Pavel Machek <pavel@ucw.cz>
Cc: "H . Peter Anvin" <hpa@zytor.com>
Cc: linux-mm@kvack.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: David Laight <David.Laight@aculab.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Eduardo Valentin <eduval@amazon.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: aliguori@amazon.com
Cc: daniel.gruss@iaik.tugraz.at
Cc: hughd@google.com
Cc: keescook@google.com
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Waiman Long <llong@redhat.com>
Cc: "David H . Gutteridge" <dhgutteridge@sympatico.ca>
Cc: joro@8bytes.org
Link: https://lkml.kernel.org/r/1531906876-13451-39-git-send-email-joro@8bytes.org

parent 7757d607

arch/x86/mm/pti.c

+22 −0

Original line number	Diff line number	Diff line
		@@ -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: */