From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45881) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1evVEu-00042d-JC for qemu-devel@nongnu.org; Mon, 12 Mar 2018 17:44:17 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1evVEq-0005qr-I8 for qemu-devel@nongnu.org; Mon, 12 Mar 2018 17:44:16 -0400 Received: from mx1.redhat.com ([209.132.183.28]:33684) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1evVEq-0005qR-A8 for qemu-devel@nongnu.org; Mon, 12 Mar 2018 17:44:12 -0400 Date: Mon, 12 Mar 2018 18:44:02 -0300 From: Eduardo Habkost Message-ID: <20180312214402.GY3417@localhost.localdomain> References: <4a65e8b30fe9d2a6c1c53b85ef2697f02e01d13f.1520867956.git.x1917x@gmail.com> <20180312194406.GX3417@localhost.localdomain> <20180313065637.00005cee@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180313065637.00005cee@gmail.com> Subject: Re: [Qemu-devel] [RFC PATCH 16/30] q35/xen: Add Xen platform device support for Q35 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alexey G Cc: xen-devel@lists.xenproject.org, qemu-devel@nongnu.org, Marcel Apfelbaum , Paolo Bonzini , Richard Henderson , "Michael S. Tsirkin" On Tue, Mar 13, 2018 at 06:56:37AM +1000, Alexey G wrote: > On Mon, 12 Mar 2018 16:44:06 -0300 > Eduardo Habkost wrote: > > >On Tue, Mar 13, 2018 at 04:34:01AM +1000, Alexey Gerasimenko wrote: > >> Current Xen/QEMU method to control Xen Platform device on i440 is a > >> bit odd -- enabling/disabling Xen platform device actually modifies > >> the QEMU emulated machine type, namely xenfv <--> pc. > >> > >> In order to avoid multiplying machine types, use a new way to > >> control Xen Platform device for QEMU -- "xen-platform-dev" machine > >> property (bool). To maintain backward compatibility with existing > >> Xen/QEMU setups, this is only applicable to q35 machine currently. > >> i440 emulation still uses the old method (i.e. xenfv/pc machine > >> selection) to control Xen Platform device, this may be changed later > >> to xen-platform-dev property as well. > >> > >> This way we can use a single machine type (q35) and change just > >> xen-platform-dev value to on/off to control Xen platform device. > >> > >> Signed-off-by: Alexey Gerasimenko > >> --- > >[...] > >> diff --git a/qemu-options.hx b/qemu-options.hx > >> index 6585058c6c..cee0b92028 100644 > >> --- a/qemu-options.hx > >> +++ b/qemu-options.hx > >> @@ -38,6 +38,7 @@ DEF("machine", HAS_ARG, QEMU_OPTION_machine, \ > >> " dump-guest-core=on|off include guest memory in > >> a core dump (default=on)\n" " mem-merge=on|off > >> controls memory merge support (default: on)\n" " > >> igd-passthru=on|off controls IGD GFX passthrough support > >> (default=off)\n" > >> + " xen-platform-dev=on|off controls Xen Platform > >> device (default=off)\n" " aes-key-wrap=on|off > >> controls support for AES key wrapping (default=on)\n" > >> " dea-key-wrap=on|off controls support for DEA key > >> wrapping (default=on)\n" " suppress-vmdesc=on|off > >> disables self-describing migration (default=off)\n" > > > >What are the obstacles preventing "-device xen-platform" from > >working? It would be better than adding a new boolean option to > >-machine. > > I guess the initial assumption was that changing the > xen_platform_device value in Xen's options may cause some additional > changes in platform configuration besides adding (or not) the Xen > Platform device, hence a completely different machine type was chosen > (xenfv). > > At the moment pc,accel=xen/xenfv selection mostly governs > only the Xen Platform device presence. Also setting max_cpus to > HVM_MAX_VCPUS depends on it, but this doesn't applicable to a > 'pc,accel=xen' machine for some reason. > > If applying HVM_MAX_VCPUS to max_cpus is really necessary I think it's > better to set it unconditionally for all 'accel=xen' HVM machine > types inside xen_enabled() block. Right now it's missing for > pc,accel=xen and q35,accel=xen. If you are talking about MachineClass::max_cpus, note that it is returned by query-machines, so it's supposed to be a static value. Changing it a runtime would mean the query-machines value is incorrect. Is HVM_MAX_CPUS higher or lower than 255? If it's higher, does it mean the current value on pc and q35 isn't accurate? > > I'll check if supplying the Xen platform device via the '-device' option > will be ok for all usage cases. Is HVM_MAX_CPUS something that needs to be enabled because of accel=xen or because or the xen-platform device? If it's just because of accel=xen, we could introduce a AccelClass::max_cpus() method (we also have KVM-imposed CPU count limits, currently implemented inside kvm_init()). -- Eduardo