From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58572) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1afm4z-0003Lx-U9 for qemu-devel@nongnu.org; Tue, 15 Mar 2016 06:20:04 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1afm4w-0001iZ-Ny for qemu-devel@nongnu.org; Tue, 15 Mar 2016 06:19:57 -0400 References: <1458021080-2145-1-git-send-email-aik@ozlabs.ru> From: Alexander Graf Message-ID: <56E7E1C5.1040409@suse.de> Date: Tue, 15 Mar 2016 11:19:49 +0100 MIME-Version: 1.0 In-Reply-To: <1458021080-2145-1-git-send-email-aik@ozlabs.ru> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH qemu] spapr/target-ppc/kvm: Only add hcall-instructions if KVM supports it List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alexey Kardashevskiy , qemu-devel@nongnu.org Cc: Paul Mackerras , qemu-ppc@nongnu.org, David Gibson On 15.03.16 06:51, Alexey Kardashevskiy wrote: > ePAPR defines "hcall-instructions" device-tree property which contains > code to call hypercalls in ePAPR paravirtualized guests. However this > property is also present for pseries guests where it does not make sense, > even though it contains dummy code which simply fails. > > Instead of maintaining the property (which used to be BE only; then was > fixed to be endian-agnostic) and confusing the guest (which might think > there is ePAPR host while there is none), this simply does not > the property to the device tree if the host kernel does not implement it. > > In order to tell the machine code if the host kernel supports > KVM_CAP_PPC_GET_PVINFO, this changes kvmppc_get_hypercall() to return 1 > if the host kernel does not implement it (which is HV KVM case). > > Signed-off-by: Alexey Kardashevskiy > --- > > > Alexander, > > We just got a bug report that LE guests would not boot under quite old QEMU > and we (powerkvm) wonder if it makes sense to backport endian-agnostic > hypercall code to older QEMU or it is simpler/more correct > not to have epapr-hypercall property in the tree. Without the property you lose KVM hypercalls, so mostly some PR speedups. For HV KVM, I don't think it makes a lot of sense to expose KVM specific hypercalls, but I'm not sure it's a great idea to block the path. With the infrastructure in place, we can at least add non-sPAPR PV if we want to. Alex