Re: [Xen-devel] Xen virtual IOMMU high level design doc V2

["Lan, Tianyu" <tianyu.lan@xxxxxxxxx>]

On 10/19/2016 4:26 AM, Konrad Rzeszutek Wilk wrote:
> On Tue, Oct 18, 2016 at 10:14:16PM +0800, Lan Tianyu wrote:
> > 1 Motivation for Xen vIOMMU
> > ===============================================================================
> > 1.1 Enable more than 255 vcpu support
> > HPC cloud service requires VM provides high performance parallel
> > computing and we hope to create a huge VM with >255 vcpu on one machine
> > to meet such requirement.Ping each vcpus on separated pcpus. More than
> > 255 vcpus support requires X2APIC and Linux disables X2APIC mode if
> > there is no interrupt remapping function which is present by vIOMMU.
> > Interrupt remapping function helps to deliver interrupt to #vcpu >255.
> > So we need to add vIOMMU before enabling >255 vcpus.
> What about Windows? Does it care about this?
From our test, win8 guest crashes when boot up 288 vcpus without IR and 
it can boot up with IR
> > 3.2 l2 translation
> > 1) For virtual PCI device
> > Xen dummy xen-vIOMMU in Qemu translates IOVA to target GPA via new
> > hypercall when DMA operation happens.
> >
> > 2) For physical PCI device
> > DMA operations go though physical IOMMU directly and IO page table for
> > IOVA->HPA should be loaded into physical IOMMU. When guest updates
> > l2 Page-table pointer field, it provides IO page table for
> > IOVA->GPA. vIOMMU needs to shadow l2 translation table, translate
> > GPA->HPA and update shadow page table(IOVA->HPA) pointer to l2
> > Page-table pointer to context entry of physical IOMMU.
> >
> > Now all PCI devices in same hvm domain share one IO page table
> > (GPA->HPA) in physical IOMMU driver of Xen. To support l2
> > translation of vIOMMU, IOMMU driver need to support multiple address
> > spaces per device entry. Using existing IO page table(GPA->HPA)
> > defaultly and switch to shadow IO page table(IOVA->HPA) when l2
> defaultly?
I mean GPA->HPA mapping will set in the assigned device's context entry 
of pIOMMU when VM creates. Just like current code works.
> > 3.3 Interrupt remapping
> > Interrupts from virtual devices and physical devices will be delivered
> > to vlapic from vIOAPIC and vMSI. It needs to add interrupt remapping
> > hooks in the vmsi_deliver() and ioapic_deliver() to find target vlapic
> > according interrupt remapping table.
> >
> >
> > 3.4 l1 translation
> > When nested translation is enabled, any address generated by l1
> > translation is used as the input address for nesting with l2
> > translation. Physical IOMMU needs to enable both l1 and l2 translation
> > in nested translation mode(GVA->GPA->HPA) for passthrough
> > device.
> >
> > VT-d context entry points to guest l1 translation table which
> > will be nest-translated by l2 translation table and so it
> > can be directly linked to context entry of physical IOMMU.
> I think this means that the shared_ept will be disabled?
The shared_ept(GPA->HPA mapping) is used to do nested translation
for any output from l1 translation(GVA->GPA).




_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel