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 X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BD300C433E0 for ; Mon, 15 Jun 2020 15:48:41 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 96DAF2078E for ; Mon, 15 Jun 2020 15:48:41 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 96DAF2078E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=citrix.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jkrLH-0001LI-23; Mon, 15 Jun 2020 15:48:11 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jkrLF-0001LD-PG for xen-devel@lists.xenproject.org; Mon, 15 Jun 2020 15:48:09 +0000 X-Inumbo-ID: 9c188d62-af1f-11ea-b80e-12813bfff9fa Received: from esa2.hc3370-68.iphmx.com (unknown [216.71.145.153]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id 9c188d62-af1f-11ea-b80e-12813bfff9fa; Mon, 15 Jun 2020 15:48:09 +0000 (UTC) Authentication-Results: esa2.hc3370-68.iphmx.com; dkim=none (message not signed) header.i=none IronPort-SDR: M5VQRtnHRZQc3T9olrbNYlwXfbbZwNmuiSAHgGezLGeSiarwyP0Fy9i4UyLhCKimEUXe2yZ2W8 LOkEDscE7ZI4mHHiEfooD+icyhInWe8nI5Wjj/erSWFgjF6ndV+03yteSwbbu3AvkZXLNPCDCH CiyBoAE4SI4ZrVpZOQCAoNWtncqJ58NxQVfBVERENejd7m3mglBFLrIjikwLIX0Xuw6/NWXtvX duN88D93Z4eNfOp64F/HJBimWIXFYHK8RUXes7PtGB0+CDRTPpAnpW3BgGwzdJrqcq8+jOiTvP +z0= X-SBRS: 2.7 X-MesageID: 20090069 X-Ironport-Server: esa2.hc3370-68.iphmx.com X-Remote-IP: 162.221.158.21 X-Policy: $RELAYED X-IronPort-AV: E=Sophos;i="5.73,515,1583211600"; d="scan'208";a="20090069" Date: Mon, 15 Jun 2020 17:47:59 +0200 From: Roger Pau =?utf-8?B?TW9ubsOp?= To: Andrew Cooper Subject: Re: [PATCH for-4.14 8/8] x86/hvm: enable emulated PIT for PVH dom0 Message-ID: <20200615154759.GH735@Air-de-Roger> References: <20200612155640.4101-1-roger.pau@citrix.com> <20200612155640.4101-9-roger.pau@citrix.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: AMSPEX02CAS02.citrite.net (10.69.22.113) To AMSPEX02CL02.citrite.net (10.69.22.126) X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: xen-devel@lists.xenproject.org, Wei Liu , Jan Beulich , paul@xen.org Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" On Mon, Jun 15, 2020 at 04:33:33PM +0100, Andrew Cooper wrote: > On 12/06/2020 16:56, Roger Pau Monne wrote: > > Some video BIOS require a PIT in order to work properly, hence classic > > PV dom0 gets partial access to the physical PIT as long as it's not in > > use by Xen. > > Is this actually true today? TBH I have no idea and asked the same thing myself. > I can believe that it may have been necessary on old hardware, but the > structure of systems has changed massively over the past 20 years, and > the PIT is very legacy these days. I also wondered whether video BIOSes really changed in the last 20 years, I really have no idea. FWIW, Wikipedia still lists PIT as being used by video BIOSes on x86 systems [0] but there are no references to specific models or video BIOSes. Alternatively we could add this as a Xen command line option, ie: dom0=pit or some such. It's however not very nice to not get output because the video BIOS doesn't function properly due to lack of PIT. Thanks, Roger. [0] https://en.wikipedia.org/wiki/Intel_8253#IBM_PC_programming_tips_and_hints