From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [PATCH v2 3/5] Qemu: do not mark bios readonly Date: Mon, 29 Oct 2012 08:44:53 +0100 Message-ID: <508E33F5.2000001@web.de> References: <50890462.5010307@linux.vnet.ibm.com> <508904C4.7030409@linux.vnet.ibm.com> <508A6772.4040400@siemens.com> <508E2B98.4050700@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enig9AED7ABEB6096619ECA35216" Cc: Avi Kivity , Marcelo Tosatti , Anthony Liguori , Kevin O'Connor , Liu Sheng , KVM , qemu-devel@nongnu.org To: Xiao Guangrong Return-path: Received: from mout.web.de ([212.227.17.12]:52800 "EHLO mout.web.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753680Ab2J2HpG (ORCPT ); Mon, 29 Oct 2012 03:45:06 -0400 In-Reply-To: <508E2B98.4050700@linux.vnet.ibm.com> Sender: kvm-owner@vger.kernel.org List-ID: This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig9AED7ABEB6096619ECA35216 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 2012-10-29 08:09, Xiao Guangrong wrote: > Jan, >=20 > On 10/26/2012 06:35 PM, Jan Kiszka wrote: >=20 >> This has two problems: We know it breaks at least Win 95 that overwrit= es >> 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. >=20 > So what is the problem? It can break Win95's running? >=20 > I tried to install win95 guest but it failed to boot regardless my patc= hset > was applied or not. I found the information that win 95 is not supporte= d at > http://www.linux-kvm.org/page/Guest_Support_Status >=20 > Note: before my patchset, Win 95 still can happily something into ROM a= rea > 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. Your patches causes regressions on TCG mode as that is perfectly fine with booting Win95 so far. >=20 >> >> 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 w= eek. >> >=20 > You idea is that modify the code of seabios and use a special way (PV) = to > notify Qemu to make the bios writable? Yes. >=20 > Actually, I am confused why the guest (including bios) persistently use= s > shadow ROM even if it is not supported (on ISA PC), i think the right w= ay > is move itself to RAM under this case, no? I've been told that Seabios has been built around that assumption and the PV shadow control would be simpler to realize. >=20 >> 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... >> >=20 > You mean that also allow Qemu to use pflash to load bios if kvm is enab= led? Yes. > 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). Isn't enabling ROMD support for KVM that whole point of your patches? I do not see yet what prevents this still, but it should be fixed first. Jan --------------enig9AED7ABEB6096619ECA35216 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.16 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://www.enigmail.net/ iEYEARECAAYFAlCOM/kACgkQitSsb3rl5xTqyQCgginuQuxmFd+4yN/1PIgOmzip IzUAoNntfMHRt9tstgbt4NfHGQQNhECE =HG2s -----END PGP SIGNATURE----- --------------enig9AED7ABEB6096619ECA35216--