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[209.132.180.67]) by mx.google.com with ESMTP id f2-v6si12482463pgh.661.2018.07.13.12.00.40; Fri, 13 Jul 2018 12:00:56 -0700 (PDT) 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; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=default header.b=Dfp0yIJa; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731555AbeGMTQA (ORCPT + 99 others); Fri, 13 Jul 2018 15:16:00 -0400 Received: from mail.kernel.org ([198.145.29.99]:40396 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731261AbeGMTQA (ORCPT ); Fri, 13 Jul 2018 15:16:00 -0400 Received: from mail-wr1-f44.google.com (mail-wr1-f44.google.com [209.85.221.44]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 68E6A208E2 for ; Fri, 13 Jul 2018 19:00:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1531508406; bh=wCj4E/GRmkGhDP2XocWWGrkQj7s61gwkL4GRxxfn1Dc=; h=In-Reply-To:References:From:Date:Subject:To:Cc:From; b=Dfp0yIJaVS+rbrY8+1k/vFGBki5dYddRmoT88nEqSVw6bMmGJAQlxHE7Fg1c+isVA YIkDzpfi0hIMSY1k1Dy9kTJuaBWxsgL6BQvgCi2v5ZFJWJawgrR00T0XHCR2iQjTpV eeZcKfKl9t5xUylhXpSORdVYAeBpX4WtV6E6wAuE= Received: by mail-wr1-f44.google.com with SMTP id b15-v6so26105781wrv.10 for ; Fri, 13 Jul 2018 12:00:06 -0700 (PDT) X-Gm-Message-State: AOUpUlG0CI3/O/W/RzD100phIu+r9LrNc4Izpb8KRE6Y5CycpTgBUXd2 55t7fT/TXnbnKz2j834DJvWocHsC+W8rFyHxYy0bHA== X-Received: by 2002:adf:e0cc:: with SMTP id e12-v6mr5628140wri.199.1531508404809; Fri, 13 Jul 2018 12:00:04 -0700 (PDT) MIME-Version: 1.0 Received: by 2002:a1c:d548:0:0:0:0:0 with HTTP; Fri, 13 Jul 2018 11:59:44 -0700 (PDT) In-Reply-To: <1531308586-29340-39-git-send-email-joro@8bytes.org> References: <1531308586-29340-1-git-send-email-joro@8bytes.org> <1531308586-29340-39-git-send-email-joro@8bytes.org> From: Andy Lutomirski Date: Fri, 13 Jul 2018 11:59:44 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 38/39] x86/mm/pti: Add Warning when booting on a PCID capable CPU To: Joerg Roedel , Borislav Petkov Cc: Thomas Gleixner , Ingo Molnar , "H . Peter Anvin" , X86 ML , LKML , Linux-MM , Linus Torvalds , Andy Lutomirski , Dave Hansen , Josh Poimboeuf , Juergen Gross , Peter Zijlstra , Jiri Kosina , Boris Ostrovsky , Brian Gerst , David Laight , Denys Vlasenko , Eduardo Valentin , Greg KH , Will Deacon , "Liguori, Anthony" , Daniel Gruss , Hugh Dickins , Kees Cook , Andrea Arcangeli , Waiman Long , Pavel Machek , "David H . Gutteridge" , Joerg Roedel Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 11, 2018 at 4:29 AM, Joerg Roedel wrote: > From: Joerg Roedel > > Warn the user in case the performance can be significantly > improved by switching to a 64-bit kernel. ... > +#ifdef CONFIG_X86_32 > + if (boot_cpu_has(X86_FEATURE_PCID)) { I'm a bit confused. Wouldn't the setup_clear_cpu_cap() call in early_identify_cpu() prevent this from working? Boris, do we have a straightforward way to ask "does the CPU advertise this feature in CPUID regardless of whether we have it enabled right now"? --Andy