[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Does a Virtual PCI Device can have MSI's
On Wed, 13 Aug 2014, manish jaggi wrote: > On 13 August 2014 19:13, Stefano Stabellini > <stefano.stabellini@xxxxxxxxxxxxx> wrote: > > On Wed, 13 Aug 2014, manish jaggi wrote: > >> On 13 August 2014 16:20, Stefano Stabellini > >> <stefano.stabellini@xxxxxxxxxxxxx> wrote: > >> > On Wed, 13 Aug 2014, manish jaggi wrote: > >> >> On 13 August 2014 15:40, Stefano Stabellini > >> >> <stefano.stabellini@xxxxxxxxxxxxx> wrote: > >> >> > On Wed, 13 Aug 2014, manish jaggi wrote: > >> >> >> Hi, > >> >> >> > >> >> >> I think it should be possible, but confirming it that this feature is > >> >> >> enabled in xen. I don't know how to test it. > >> >> >> > >> >> >> Does any virtual PCI device in DomU (I don't mean a virtual function) > >> >> >> have MSI interrupts ? > >> >> > > >> >> > Yes, they do. > >> >> > > >> >> > > >> >> >> If yes then how is that MSI handled in Xen > >> >> > > >> >> > PV guests on x86 don't receive MSIs or legacy interrupts as is. They > >> >> > map them into "pirqs" instead, that are a kind of event channels, Xen > >> >> > specific software interrupts. For each MSI on the PCI device assigned > >> >> > to > >> >> > the guest, the guest kernel would ask for a pirq, see: > >> >> > > >> >> > arch/x86/pci/xen.c:xen_pcifront_enable_irq > >> >> > arch/x86/pci/xen.c:xen_setup_msi_irqs > >> >> > > >> >> > In the specific case of MSIs and MSI-X, pcifront issues an hypercall > >> >> > in > >> >> > order to enable them, see: > >> >> > > >> >> > drivers/pci/xen-pcifront.c:pci_frontend_enable_msi > >> >> > > >> >> > and the backend returns the pirq number: > >> >> > > >> >> > drivers/xen/xen-pciback/pciback_ops.c:xen_pcibk_enable_msi > >> >> > > >> >> > > >> >> > On ARM I think it would be best if we delivered MSIs as MSIs to the > >> >> > guest, rather than mapping them into pirqs, to take better advantage > >> >> > of > >> >> > the hardware. But it would be up to you to change the pcifront/pciback > >> >> > code to do it. > >> >> > In first instance it would be fine if we end up using pirqs. > >> >> > >> >> I am considering 2 cases here > >> >> a) physical PCI passthrough devices / functions assigned to domU > >> > > >> > Are you sure you mean DomU here, or maybe you mean Dom0? > >> > > >> Yes DomU only. > >> > > >> >> b) emulated (virtual) PCI devices assigned to domU > >> > > >> > We need to clarify the terminology here: what do you mean by (b)? > >> > Emulating an entire PCI device and exposing it to domU? Why do you want > >> > to do that? It is not a feature I am keen on having on Xen on ARM. > >> > Otherwise if you are thinking of a virtual function of an SR-IOV card, > >> > that is still (a) from the Xen point of view. > >> > >> I was trying to understand that does Xen support some device like a > >> sata device which is a virtual one emulated using qemu on a PV domU > >> and its interrupts are MSIs > > > > I wouldn't want to support this use case at all, unless strictly > > necessary: emulation is slower and less secure (larger surface of > > attack) than PV interfaces. > > > Thats why I asked this question, if a virtual device is assigned to a > domU how would the MSIs be configured for it, using front-back > communication or using the Linux ITS driver which gets trapped into > Xens ITS driver. If it is an emulated device, by definition there is no front-back communication. > >> >> For (a) it is straight to configure and inject the MSI into guest > >> > > >> > Yep, that is what I was trying to say. > >> > > >> > > >> >> For (b) how does the configuring and injection should work, > >> >> - PCI Front driver using backops requests to enable msi > >> >> - At a later stage xen using dom0 (somehow) inject an virtual LPI into > >> >> domU. > >> >> > >> >> What are your thoughts on this? > >> > > >> > I am not sure I understand what you mean by (b) anymore. In fact > >> > pcifront is used to deal with PCI passthrough to DomUs, that would be > >> > (a) by your description. > >> > _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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