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Subject: Re: [PATCH 34/34] x86/mm/pti: Add Warning when booting on a PCIE
 capable CPU
To:     Joerg Roedel <joro@8bytes.org>,
        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>,
        jroedel@suse.de
References: <1520245563-8444-1-git-send-email-joro@8bytes.org>
 <1520245563-8444-35-git-send-email-joro@8bytes.org>
From:   Waiman Long <longman@redhat.com>
Organization: Red Hat
Message-ID: <d879496a-887d-9077-3a7d-ee878a691bdc@redhat.com>
Date:   Mon, 5 Mar 2018 08:39:28 -0500
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On 03/05/2018 05:26 AM, Joerg Roedel wrote:
> 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 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();

Typo in the patch title: PCIE => PCID.

-Longman