From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xiao Guangrong Subject: Re: [PATCH v2 3/5] Qemu: do not mark bios readonly Date: Mon, 29 Oct 2012 15:09:12 +0800 Message-ID: <508E2B98.4050700@linux.vnet.ibm.com> References: <50890462.5010307@linux.vnet.ibm.com> <508904C4.7030409@linux.vnet.ibm.com> <508A6772.4040400@siemens.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: Avi Kivity , Marcelo Tosatti , Anthony Liguori , "Kevin O'Connor" , Liu Sheng , KVM , qemu-devel@nongnu.org To: Jan Kiszka Return-path: Received: from e28smtp05.in.ibm.com ([122.248.162.5]:57264 "EHLO e28smtp05.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750942Ab2J2HJ0 (ORCPT ); Mon, 29 Oct 2012 03:09:26 -0400 Received: from /spool/local by e28smtp05.in.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 29 Oct 2012 12:39:23 +0530 Received: from d28av01.in.ibm.com (d28av01.in.ibm.com [9.184.220.63]) by d28relay01.in.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id q9T79JKI39845918 for ; Mon, 29 Oct 2012 12:39:19 +0530 Received: from d28av01.in.ibm.com (loopback [127.0.0.1]) by d28av01.in.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id q9TCdAn7018188 for ; Mon, 29 Oct 2012 12:39:11 GMT In-Reply-To: <508A6772.4040400@siemens.com> Sender: kvm-owner@vger.kernel.org List-ID: Jan, On 10/26/2012 06:35 PM, Jan Kiszka wrote: > This has two problems: We know it breaks at least Win 95 that overwrites > its F-segment during boot. And it applies changes to the shadowed area > (below 1 MB) also to the ROM area - I don't think that is the original > behaviour on real hardware. So what is the problem? It can break Win95's running? I tried to install win95 guest but it failed to boot regardless my patchset was applied or not. I found the information that win 95 is not supported at http://www.linux-kvm.org/page/Guest_Support_Status Note: before my patchset, Win 95 still can happily something into ROM area because readonly memory is actually writable on KVM. And win95 can not run on isapc with --no-kvm since it is no way to enable shadow ROM. > > What we need is paravirtual shadow write control for the ISA PC. It's on > my todo list, maybe I will be able to look into this during the next week. > You idea is that modify the code of seabios and use a special way (PV) to notify Qemu to make the bios writable? Actually, I am confused why the guest (including bios) persistently uses shadow ROM even if it is not supported (on ISA PC), i think the right way is move itself to RAM under this case, no? > BTW, your patch series should allow to drop the KVM special case from > pc_system_firmware_init. That version, btw, treats high and low BIOS > areas separately - but only reloads the upper area. Hmm... > You mean that also allow Qemu to use pflash to load bios if kvm is enabled? We can not do that for pflash is a RD device which can not be directly written, kvm can not emulate the instruction which implicitly write the memory. (e.g: using this area as stack). Thanks!