Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753858Ab0LFQfE (ORCPT ); Mon, 6 Dec 2010 11:35:04 -0500 Received: from thoth.sbs.de ([192.35.17.2]:18772 "EHLO thoth.sbs.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752421Ab0LFQfC (ORCPT ); Mon, 6 Dec 2010 11:35:02 -0500 Message-ID: <4CFD108F.5000200@siemens.com> Date: Mon, 06 Dec 2010 17:34:23 +0100 From: Jan Kiszka User-Agent: Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv:1.8.1.12) Gecko/20080226 SUSE/2.0.0.12-1.1 Thunderbird/2.0.0.12 Mnenhy/0.7.5.666 MIME-Version: 1.0 To: Avi Kivity CC: Jan Kiszka , Thomas Gleixner , Marcelo Tosatti , "linux-kernel@vger.kernel.org" , kvm , Tom Lyon , Alex Williamson , "Michael S. Tsirkin" Subject: Re: [PATCH 5/5] KVM: Allow host IRQ sharing for passed-through PCI 2.3 devices References: <10b9265d513950f2574edf4e79be3b808e741a78.1291419444.git.jan.kiszka@web.de> <4CFD0D91.3050303@redhat.com> In-Reply-To: <4CFD0D91.3050303@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3381 Lines: 82 Am 06.12.2010 17:21, Avi Kivity wrote: > 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? Userspace just has to synchronize against itself - what it already does: qemu_mutex, and masking/unmasking is synchronous /wrt the the executing VCPU. Otherwise, masking/unmasking is naturally racy, also in Real Life. The guest resolves the remaining races. > > Isn't there a race window between the two operations? > > Maybe we should give the kernel full ownership of that bit. I think this is what VFIO does and is surely cleaner than this approach. But it's not possible with the existing interface (sysfs + KVM ioctls) - or can you restrict the sysfs access to the config space in such details? Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux -- 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/