Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759517Ab3EGJaw (ORCPT ); Tue, 7 May 2013 05:30:52 -0400 Received: from smtp.eu.citrix.com ([46.33.159.39]:20646 "EHLO SMTP.EU.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759277Ab3EGJau (ORCPT ); Tue, 7 May 2013 05:30:50 -0400 X-IronPort-AV: E=Sophos;i="4.87,552,1363132800"; d="scan'208";a="4290601" Message-ID: <1367919047.26321.47.camel@zakaz.uk.xensource.com> Subject: Re: [Xen-devel] [PATCH 2/4] xen/vcpu: Document the xen_vcpu_info and xen_vcpu From: Ian Campbell To: Konrad Rzeszutek Wilk CC: "linux-kernel@vger.kernel.org" , "xen-devel@lists.xensource.com" , Stefano Stabellini Date: Tue, 7 May 2013 10:30:47 +0100 In-Reply-To: <1367845498-14290-3-git-send-email-konrad.wilk@oracle.com> References: <1367845498-14290-1-git-send-email-konrad.wilk@oracle.com> <1367845498-14290-3-git-send-email-konrad.wilk@oracle.com> Organization: Citrix Systems, Inc. Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.4.4-1 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2800 Lines: 70 On Mon, 2013-05-06 at 14:04 +0100, Konrad Rzeszutek Wilk wrote: > They are important structures and it is not clear at first > look what they are for. > > The xen_vcpu is a pointer. By default it points to the shared_info > structure (at the CPU offset location). However if the > VCPUOP_register_vcpu_info hypercall is implemented we can make the > xen_vcpu pointer point to a per-CPU location. > > Signed-off-by: Konrad Rzeszutek Wilk > --- > arch/x86/xen/enlighten.c | 21 ++++++++++++++++++++- > 1 file changed, 20 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c > index 94a81f4..9b34475 100644 > --- a/arch/x86/xen/enlighten.c > +++ b/arch/x86/xen/enlighten.c > @@ -85,7 +85,21 @@ > > EXPORT_SYMBOL_GPL(hypercall_page); > > +/* > + * Pointer to the xen_vcpu_info structure or > + * &HYPERVISOR_shared_info->vcpu_info[cpu]. See xen_hvm_init_shared_info > + * and xen_vcpu_setup for details. By default it points to share_info->vcpu_info > + * but if the hypervisor supports VCPUOP_register_vcpu_info then it can point > + * to xen_vcpu_info. The pointer is used in __xen_evtchn_do_upcall to > + * acknowledge pending events. Also more subtly it is used by the patched version of irq enable/disable e.g. xen_irq_enable_direct and xen_iret. The desire to be able to do those mask/unmask operations as a single instruction by using the per-cpu offset held in %gs is the real reason vcpu info is in a per-cpu pointer and for the whole register_vcpu_info thing IIRC. > + */ > DEFINE_PER_CPU(struct vcpu_info *, xen_vcpu); > + > +/* > + * Per CPU pages used if hypervisor supports VCPUOP_register_vcpu_info > + * hypercall. This can be used both in PV and PVHVM mode. The structure > + * overrides the default per_cpu(xen_vcpu, cpu) value. > + */ > DEFINE_PER_CPU(struct vcpu_info, xen_vcpu_info); > > enum xen_domain_type xen_domain_type = XEN_NATIVE; > @@ -187,7 +201,12 @@ static void xen_vcpu_setup(int cpu) > > /* Check to see if the hypervisor will put the vcpu_info > structure where we want it, which allows direct access via > - a percpu-variable. */ > + a percpu-variable. > + N.B. This hypercall can _only_ be called once per CPU. Subsequent > + calls will error out with -EINVAL. This is due to the fact that > + hypervisor has no unregister variant and this hypercall does not > + allow to over-write info.mfn and info.offset. > + */ > err = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_info, cpu, &info); > > if (err) { -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/