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Re: [Xen-devel] Re: Accessing PCI BAR space directly from XEN hypervisor

  • To: veerasena reddy <veeruyours@xxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: Keir Fraser <keir.xen@xxxxxxxxx>
  • Date: Tue, 14 Jun 2011 07:38:55 +0100
  • Cc:
  • Delivery-date: Mon, 13 Jun 2011 23:39:51 -0700
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  • Thread-topic: [Xen-devel] Re: Accessing PCI BAR space directly from XEN hypervisor

On 14/06/2011 04:25, "veerasena reddy" <veeruyours@xxxxxxxxx> wrote:

> Hi,
> Can someone please throw some light on this
> Thanks in advance.

You'll have to set up a fixmap slot and use set_fixmap and fix_to_virt. Xen
doesn't have ioremap.

 -- Keir

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