From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 5/5] KVM: Allow host IRQ sharing for passed-through PCI 2.3 devices Date: Mon, 06 Dec 2010 18:21:37 +0200 Message-ID: <4CFD0D91.3050303@redhat.com> References: <10b9265d513950f2574edf4e79be3b808e741a78.1291419444.git.jan.kiszka@web.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Thomas Gleixner , Marcelo Tosatti , linux-kernel@vger.kernel.org, kvm , Tom Lyon , Alex Williamson , "Michael S. Tsirkin" , Jan Kiszka To: Jan Kiszka Return-path: In-Reply-To: <10b9265d513950f2574edf4e79be3b808e741a78.1291419444.git.jan.kiszka@web.de> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 12/04/2010 01:37 AM, Jan Kiszka wrote: > From: Jan Kiszka > > PCI 2.3 allows to generically disable IRQ sources at device level. This > enables us to share IRQs of such devices on the host side when passing > them to a guest. > > However, IRQ disabling via the PCI config space is more costly than > masking the line via disable_irq. Therefore we register an IRQ sharing > notifier and switch between line and device level disabling on demand. > > This feature is optional, user space has to request it explicitly as it > also has to inform us about its view of PCI_COMMAND_INTX_DISABLE. That > way, we can avoid unmasking the interrupt and signaling it if the guest > masked it via the PCI config space. > > > diff --git a/Documentation/kvm/api.txt b/Documentation/kvm/api.txt > index e1a9297..5e164db 100644 > --- a/Documentation/kvm/api.txt > +++ b/Documentation/kvm/api.txt > @@ -1112,6 +1112,14 @@ following flags are specified: > > /* Depends on KVM_CAP_IOMMU */ > #define KVM_DEV_ASSIGN_ENABLE_IOMMU (1<< 0) > +/* The following two depend on KVM_CAP_PCI_2_3 */ > +#define KVM_DEV_ASSIGN_PCI_2_3 (1<< 1) > +#define KVM_DEV_ASSIGN_MASK_INTX (1<< 2) > + > +If KVM_DEV_ASSIGN_PCI_2_3 is set, the kernel will manage legacy INTx interrupts > +via the PCI-2.3-compliant device-level mask, but only if IRQ sharing with other > +assigned or host devices requires it. KVM_DEV_ASSIGN_MASK_INTX specifies the > +guest's view on the INTx mask, see KVM_ASSIGN_SET_INTX_MASK for details. > > 4.48 KVM_DEASSIGN_PCI_DEVICE > > @@ -1263,6 +1271,23 @@ struct kvm_assigned_msix_entry { > __u16 padding[3]; > }; > > +4.54 KVM_ASSIGN_SET_INTX_MASK > + > +Capability: KVM_CAP_PCI_2_3 > +Architectures: x86 > +Type: vm ioctl > +Parameters: struct kvm_assigned_pci_dev (in) > +Returns: 0 on success, -1 on error > + > +Informs the kernel about the guest's view on the INTx mask. As long as the > +guest masks the legacy INTx, the kernel will refrain from unmasking it at > +hardware level and will not assert the guest's IRQ line. User space is still > +responsible for applying this state to the assigned device's real config space. What's the protocol for doing this? I suppose userspace has to disable interrupts, ioctl(SET_INTX_MASK, masked), ..., ioctl(SET_INTX_MASK, unmasked), enable interrupts? Isn't there a race window between the two operations? Maybe we should give the kernel full ownership of that bit. > + > +See KVM_ASSIGN_DEV_IRQ for the data structure. The target device is specified > +by assigned_dev_id. In the flags field, only KVM_DEV_ASSIGN_MASK_INTX is > +evaluated. > + -- error compiling committee.c: too many arguments to function