Re: Accessing PCI BAR space directly from XEN hypervisor

[veerasena reddy <veeruyours@gmail.com>]

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Hi,

Can someone please throw some light on this

Thanks in advance.

Regards,
VSR.
On Mon, Jun 13, 2011 at 2:24 PM, veerasena reddy <veeruyours@gmail.com>wrote:

> Hi,
>
> I am doing an experiment to see if I can get more throughput by moving the
> Tx ring update and doorbell ring mechanism to hypervisor and provide a
> hypercall to HVM Guest. When there is a Tx packet ready, the HVM guest
> invokes the hypercall along with the packet address as argument. The
> hypercall function will write the packet address to the Tx ring and rings
> the doorbell directly without involving dom0.
>
> AS part of this, i need to access IO Memory BAR region of the PCI network
> device from XEN hypervisor (hypercall handler). For this, i tried converting
> the BAR Physical address (captured from lspci as shown below) of the PCI
> device to MFN, but got all F's (invalid entry). Even pfn_valid(0xf0904000)
> failed on this address. Where as I could successfully map a dom0 page
> (allocated using vmalloc()) and access in hypervisor using
> map_domain_page(mfn).
>
> Could any one please suggest how to access the BAR regions of a PCI device
> from hypervisor? how to do mapping and read/write operations?
>
> Also, Could you please explain the difference between mapping locally
> allocated pages and PCI BAR memory of dom0 in hypervisor?
>
> Thanks in advance.
>
> Regards,
> VSR.
> ==========================
> [root@fc13 xen]# lspci -vvs 09:00.0
> 09:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168B
> PCI Express Gigabit Ethernet controller (rev 03)
>     Subsystem: Lenovo Device 2131
>     Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr-
> Stepping- SERR+ FastB2B- DisINTx+
>     Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort-
> <MAbort- >SERR- <PERR- INTx-
>     Latency: 0, Cache Line Size: 64 bytes
>     Interrupt: pin A routed to IRQ 1247
>     Region 0: I/O ports at 4000 [size=256]
>     Region 2: Memory at f0904000 (64-bit, prefetchable) [size=4K]
>     Region 4: Memory at f0900000 (64-bit, prefetchable) [size=16K]
>     [virtual] Expansion ROM at f0920000 [disabled] [size=128K]
> ===========================
>

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