From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-f193.google.com ([209.85.220.193]:38455 "EHLO mail-qk0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751038AbeDEO44 (ORCPT ); Thu, 5 Apr 2018 10:56:56 -0400 Received: by mail-qk0-f193.google.com with SMTP id 132so26623456qkd.5 for ; Thu, 05 Apr 2018 07:56:56 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <9fb78740-33a1-76f8-4a7d-e7713c3b8078@suse.com> References: <20180404142702.GA20460@kroah.com> <20180404144644.GA22656@kroah.com> <20180404154201.GA31981@kroah.com> <9cd0be43-6380-f5a0-0427-7f75fca966a9@suse.com> <20180405063314.GC5431@kroah.com> <20180405071448.GA9183@kroah.com> <950f2f68-04ef-bf4d-fa61-afa9bdc918e4@suse.com> <4bf257f2-dad7-62d2-ad5b-8972c0311119@suse.com> <9fb78740-33a1-76f8-4a7d-e7713c3b8078@suse.com> From: George Dunlap Date: Thu, 5 Apr 2018 15:56:54 +0100 Message-ID: Subject: Re: [Xen-devel] Patches for stable To: Juergen Gross Cc: Greg KH , Boris Ostrovsky , stable , xen-devel Content-Type: text/plain; charset="UTF-8" Sender: stable-owner@vger.kernel.org List-ID: On Thu, Apr 5, 2018 at 3:09 PM, Juergen Gross wrote: > On 05/04/18 15:42, George Dunlap wrote: >> On Thu, Apr 5, 2018 at 2:06 PM, Juergen Gross wrote: >>> On 05/04/18 15:00, Boris Ostrovsky wrote: >>>> On 04/05/2018 08:19 AM, Juergen Gross wrote: >>>>> On 05/04/18 12:06, George Dunlap wrote: >>>>> >>>>>> Aren't there flags in the binary somewhere that could tell the >>>>>> toolstack / Xen whether the kernel in question needs the RSDP table in >>>>>> lowmem, or whether it can be put higher? >>>>> Not really. Analyzing the binary whether it accesses the rsdp_addr in >>>>> the start_info isn't the way to go, IMO. >>>>> >>>>> I've sent a patch to xen-devel adding a quirk flag to the domain's >>>>> config to enable the admin special casing such an "old" kernel. >>>> >>>> Can we backport latest struct hvm_start_info changes (which bumped >>>> interface version) to 4.11 and pass RSDP only for versions >=1? >>> >>> And this would help how? >>> >>> RSDP address is passed today, the kernel just doesn't read it. And >>> how should Xen know which interface version the kernel is supporting? >>> And Xen needs to know that in advance in order to place the RSDP in >>> low memory in case the kernel isn't reading the RSDP address from >>> start_info. >> >> But the kernel image has ELF notes, right? You can put one that >> indicates that this binary *does* know how to read the RSDP from the >> start_info, and if you don't find that, put it in lowmem. > > Sow you would hurt BSD which does read the RSDP address correctly but > (today) has no such ELF note. > > I think extending the PVH interface in such a way is no good idea. Option 1: Put the RSDP in lowmem unless we know the guest will use the address in start_info Pro: Existing Linux instances boot Con: Existing BSD instances whose memory is an exact multiple of 1 GiB will have slightly slower TLB miss times. Option 2: Put the RSDP in highmem regardless Pro: Existing BSD instances whose memory is an exact multiple of 1GiB will have slightly faster TLB miss times Con: Existing Linux instances don't boot at all This seems like a no-brainer to me. But anyway, maybe we should move the discussion elsewhere and stop bothering Greg. :-) -George