From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 08/26] KVM: PPC: Add PV guest critical sections Date: Sun, 27 Jun 2010 12:52:26 +0300 Message-ID: <4C271F5A.1030409@redhat.com> References: <1277508314-915-1-git-send-email-agraf@suse.de> <1277508314-915-9-git-send-email-agraf@suse.de> <4C2709F4.10805@redhat.com> <77DBE095-884F-4986-BE2B-15B2EEAD8CAC@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Cc: linuxppc-dev , KVM list , "kvm-ppc@vger.kernel.org" To: Alexander Graf Return-path: In-Reply-To: <77DBE095-884F-4986-BE2B-15B2EEAD8CAC@suse.de> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linuxppc-dev-bounces+glppe-linuxppc-embedded-2=m.gmane.org@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+glppe-linuxppc-embedded-2=m.gmane.org@lists.ozlabs.org List-Id: kvm.vger.kernel.org On 06/27/2010 12:40 PM, Alexander Graf wrote: > > Am 27.06.2010 um 10:21 schrieb Avi Kivity : > >> On 06/26/2010 02:24 AM, Alexander Graf wrote: >>> When running in hooked code we need a way to disable interrupts without >>> clobbering any interrupts or exiting out to the hypervisor. >>> >>> To achieve this, we have an additional critical field in the shared >>> page. If >>> that field is equal to the r1 register of the guest, it tells the >>> hypervisor >>> that we're in such a critical section and thus may not receive any >>> interrupts. >>> >> >> Is r1 reserved for this purpose? Can't it match accidentally? > > r1 is defined by the abi to be the stack. Neat trick! >> >> Why won't zero/nonzero work for this? > > Because there is no store immediate opcode on powerpc :(. Or inc/dec... -- error compiling committee.c: too many arguments to function