From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4DAA6C433EF for ; Mon, 11 Jul 2022 11:18:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230251AbiGKLSe (ORCPT ); Mon, 11 Jul 2022 07:18:34 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58874 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231179AbiGKLSP (ORCPT ); Mon, 11 Jul 2022 07:18:15 -0400 Received: from mail.skyhub.de (mail.skyhub.de [IPv6:2a01:4f8:190:11c2::b:1457]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0CD69747A3 for ; Mon, 11 Jul 2022 03:40:32 -0700 (PDT) Received: from zn.tnic (p200300ea970ff601329c23fffea6a903.dip0.t-ipconnect.de [IPv6:2003:ea:970f:f601:329c:23ff:fea6:a903]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 964B31EC0518; Mon, 11 Jul 2022 12:40:26 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1657536026; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:in-reply-to:in-reply-to: references:references; bh=DQveIvP21h/SanKF+N0Kr1ZyhDAmgYuWOYIW71suvFg=; b=CnP+YTdQFXXeMz4yz7lRKZrtDOotgh/qmneigxkyjFPzRx22eIHesEikobYkfzhA0eFGHx bgWLcABXTonqdCSQS/VeaNriU3qJ60lGziMlFEFviVrJ4ncqEsKyuMs/HXtUf2QXs9ucao boRyB8MdlK+myKDMfvTxFNaK5ZPE7Hk= Date: Mon, 11 Jul 2022 12:40:26 +0200 From: Borislav Petkov To: Jan Beulich Cc: Andrew Lutomirski , "dave.hansen@linux.intel.com" , Peter Zijlstra , lkml , "xen-devel@lists.xenproject.org" Subject: Re: [PATCH] x86/PAT: have pat_enabled() properly reflect state when running on e.g. Xen Message-ID: References: <9385fa60-fa5d-f559-a137-6608408f88b0@suse.com> <016d281b-7e40-f1bd-66ee-c19c3cc56efe@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 07, 2022 at 08:38:44AM +0200, Jan Beulich wrote: > Well, right now the pvops hook for Xen swallows #GP anyway (wrongly > so imo, but any of my earlier pointing out of that has been left > unheard, despite even the code comments there saying "It may be worth > changing that"). Oh great. ;-\ > The point is therefore that after writing PAT, it would need reading > back. In which case it feels (slightly) more clean to me to avoid the > write attempt in the first place, when we know it's not going to work. X86_FEATURE_XENPV check then. > If I may ask - doesn't this mean this patch, in its current shape, is > already a (small) step in that direction? In any event what you say > doesn't sound to me like a viable (backportable) route to addressing > the regression at hand. Backportable to where? To whatever tree has bdd8b6c98239 ("drm/i915: replace X86_FEATURE_PAT with pat_enabled()") ? If it is that, then 5.17 and newer. Anyway, I don't mind it as long as you put the proper splitting out ontop and it all goes as a single patchset, with the minimal fix CC:stable and queued first. Thx. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette