Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Joerg Roedel <joro@8bytes.org>
To:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>,
        "H . Peter Anvin" <hpa@zytor.com>
Cc:     x86@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Juergen Gross <jgross@suse.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Borislav Petkov <bp@alien8.de>, Jiri Kosina <jkosina@suse.cz>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Brian Gerst <brgerst@gmail.com>,
        David Laight <David.Laight@aculab.com>,
        Denys Vlasenko <dvlasenk@redhat.com>,
        Eduardo Valentin <eduval@amazon.com>,
        Greg KH <gregkh@linuxfoundation.org>,
        Will Deacon <will.deacon@arm.com>, aliguori@amazon.com,
        daniel.gruss@iaik.tugraz.at, hughd@google.com, keescook@google.com,
        Andrea Arcangeli <aarcange@redhat.com>,
        Waiman Long <llong@redhat.com>, Pavel Machek <pavel@ucw.cz>,
        "David H . Gutteridge" <dhgutteridge@sympatico.ca>,
        jroedel@suse.de, joro@8bytes.org
Subject: [PATCH 34/35] x86/mm/pti: Add Warning when booting on a PCID capable CPU
Date:   Mon, 16 Apr 2018 17:25:22 +0200
Message-Id: <1523892323-14741-35-git-send-email-joro@8bytes.org>
In-Reply-To: <1523892323-14741-1-git-send-email-joro@8bytes.org>
References: <1523892323-14741-1-git-send-email-joro@8bytes.org>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

From: Joerg Roedel <jroedel@suse.de>

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>
---
 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 60a1ee0..ad905e0 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -497,6 +497,22 @@ 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();
 
 	/* Undo all global bits from the init pagetables in head_64.S: */
-- 
2.7.4