From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:44070) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dH3bz-0002Pw-3L for qemu-devel@nongnu.org; Sat, 03 Jun 2017 03:36:40 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dH3bw-00082N-0s for qemu-devel@nongnu.org; Sat, 03 Jun 2017 03:36:39 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56284) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dH3bv-00081W-R5 for qemu-devel@nongnu.org; Sat, 03 Jun 2017 03:36:35 -0400 From: Laszlo Ersek References: Message-ID: <2ff62b03-d71b-93c4-79bf-10682b229758@redhat.com> Date: Sat, 3 Jun 2017 09:36:23 +0200 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] allocation zone extensions for the firmware linker/loader List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: SeaBIOS devel list , qemu devel list , edk2-devel-ml01 Cc: Kevin O'Connor , "Michael S. Tsirkin" , Ard Biesheuvel , Ben Warren , Dongjiu Geng , Igor Mammedov , "Jordan Justen (Intel address)" , "Leif Lindholm (Linaro address)" , Shannon Zhao , Stefan Berger , Xiao Guangrong , "Dr. David Alan Gilbert" , Gerd Hoffmann On 06/02/17 17:45, Laszlo Ersek wrote: > The patches can cause linker/loader breakage when old firmware is booted > on new QEMU. However, that's no problem (it's nothing new), the next > release of QEMU should bundle the new firmware binaries as always. Dave made a good point (which I should have realized myself, really!), namely if you launch old fw on old qemu, then migrate the guest to a new qemu and then reboot the guest on the target host, within the migrated VM, things will break. So that makes this approach dead in the water. Possible mitigations I could think of: - Make it machine type dependent. Complicated (we don't usually bind ACPI generation to machine types) and wouldn't help existing devices. - Let the firmware negotiate these extensions. Very complicated (new fw-cfg files are needed for negotiation) and wouldn't help existing devices. So I guess I'll do what Igor and Gerd suggested: record in advance whether any pointer field narrower than 8 bytes points into a given blob, and if so, forbid allocating that blob from 64-bit address space. This should solve Ard's needs purely within the firmware. Regarding the NOACPI hint, I guess I'm dropping that. I only meant NOACPI for addressing Igor's long-standing dislike for the "ACPI SDT header probe suppression" in VMGENID (and future similar devices). But, there's no actual *technical* need to eliminate that (unlike the technical need for 64-bit blob allocations which should really be solved), so I guess it's OK to postpone NOACPI indefinitely. Self-nack for this set of sets. Thanks for the feedback, Laszlo