Mailing List Archive: Pinning a DomU Guest data page from Hypervisor

Pinning a DomU Guest data page from Hypervisor

Aug 3, 2011, 6:56 AM

Post #1 of 6 (268 views)

Hi,

I have a DomU Guest (PVHVM) running a customized PV network driver. To
increase the network IO performance I would like to try providing the
address of the Guest pages directly to the network device without involving
dom0.
For this i need to convert the GMFN of the page to MFN in hypervisor and pin
the page. I could map the device BAR to hypervisor and write the Guest
addresses to device. But I couldn't get how to Pin the Guest pages.

I looked into code "xen/arch/x86/mm.c", do_mmuext_op() which was
invoking xsm_memory_pin_page() only for L1 to L4 page table type pages. Can
i use the same API to pin data pages?

Could anybody please advice how can I pin a Guest data page from hypervisor.
Any APIs or sequence of operations to be done on MFN of the guest page?

Thanks & Regards,
VSR.

Re: Pinning a DomU Guest data page from Hypervisor [ In reply to ]

pasik at iki

Aug 3, 2011, 10:09 AM

Post #2 of 6 (269 views)

Permalink

On Wed, Aug 03, 2011 at 07:26:47PM +0530, veerasena reddy wrote:
> Hi,
> I have a DomU Guest (PVHVM) running a customized PV network driver. To
> increase the network IO performance I would like to try providing the
> address of the Guest pages directly to the network device without
> involving dom0.

Hmm.. can't you use IOMMU PCI passthru?
http://wiki.xen.org/xenwiki/XenPCIpassthrough

-- Pasi

> For this i need to convert the GMFN of the page to MFN in hypervisor and
> pin the page. I could map the device BAR to hypervisor and write the Guest
> addresses to device. But I couldn't get how to Pin the Guest pages.
> I looked into code "xen/arch/x86/mm.c", do_mmuext_op() which was
> invoking xsm_memory_pin_page() only for L1 to L4 page table type pages.
> Can i use the same API to pin data pages?
> Could anybody please advice how can I pin a Guest data page from
> hypervisor. Any APIs or sequence of operations to be done on MFN of the
> guest page?
> Thanks & Regards,
> VSR.

> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel

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Re: Pinning a DomU Guest data page from Hypervisor [ In reply to ]

tim at xen

Aug 3, 2011, 10:16 AM

Post #3 of 6 (268 views)

Permalink

Hi,

At 19:26 +0530 on 03 Aug (1312399607), veerasena reddy wrote:
> I looked into code "xen/arch/x86/mm.c", do_mmuext_op() which was
> invoking xsm_memory_pin_page() only for L1 to L4 page table type pages. Can
> i use the same API to pin data pages?
>
> Could anybody please advice how can I pin a Guest data page from hypervisor.
> Any APIs or sequence of operations to be done on MFN of the guest page?

What exactly do you mean by "pin"? If you mean stop the guest OS from
paging out the contents, that can't be done from inside the hypervisor.
If you mean keep it from being used as a pagetable, LDT or other special
page, that can be done with get_page_and_type(), but you still need the
guest OS to cooperate.

Tim.

--
Tim Deegan <tim@xen.org>
Principal Software Engineer, Xen Platform Team
Citrix Systems UK Ltd. (Company #02937203, SL9 0BG)

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Re: Pinning a DomU Guest data page from Hypervisor [ In reply to ]

veeruyours at gmail

Aug 3, 2011, 10:50 AM

Post #4 of 6 (268 views)

Permalink

Hi,

Thanks for the response.

By pinning, I mean to keep the data page always in main memory for the
device to access. Once the device processes the page, i can unpin.
Please correct me, if i understood page pinning concept wrongly.
But, my goal is to keep the page in main memory until the device processes
it.
Please advice.

Thanks & Regards,
VSR.
On Wed, Aug 3, 2011 at 10:46 PM, Tim Deegan <tim@xen.org> wrote:

> Hi,
>
> At 19:26 +0530 on 03 Aug (1312399607), veerasena reddy wrote:
> > I looked into code "xen/arch/x86/mm.c", do_mmuext_op() which was
> > invoking xsm_memory_pin_page() only for L1 to L4 page table type pages.
> Can
> > i use the same API to pin data pages?
> >
> > Could anybody please advice how can I pin a Guest data page from
> hypervisor.
> > Any APIs or sequence of operations to be done on MFN of the guest page?
>
> What exactly do you mean by "pin"? If you mean stop the guest OS from
> paging out the contents, that can't be done from inside the hypervisor.
> If you mean keep it from being used as a pagetable, LDT or other special
> page, that can be done with get_page_and_type(), but you still need the
> guest OS to cooperate.
>
> Tim.
>
> --
> Tim Deegan <tim@xen.org>
> Principal Software Engineer, Xen Platform Team
> Citrix Systems UK Ltd. (Company #02937203, SL9 0BG)
>

Re: Pinning a DomU Guest data page from Hypervisor [ In reply to ]

tim at xen

Aug 3, 2011, 11:13 AM

Post #5 of 6 (264 views)

Permalink

Hi,

At 23:20 +0530 on 03 Aug (1312413612), veerasena reddy wrote:
> By pinning, I mean to keep the data page always in main memory for the
> device to access. Once the device processes the page, i can unpin.
> Please correct me, if i understood page pinning concept wrongly.
> But, my goal is to keep the page in main memory until the device processes
> it.

If you want to stop _xen_ reassigning this frame (including any
hypervisor-level paging) you can just take a reference count (probably
you want a writeable-tyrp typecount using get_page_and_type()). But Xen
can't stop the guest OS from reusing the frame (including paging its
contents out), so you will need to address that inside the guest OS.

Tim.

--
Tim Deegan <tim@xen.org>
Principal Software Engineer, Xen Platform Team
Citrix Systems UK Ltd. (Company #02937203, SL9 0BG)

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Xen-devel mailing list
Xen-devel@lists.xensource.com
http://lists.xensource.com/xen-devel

Re: Pinning a DomU Guest data page from Hypervisor [ In reply to ]

veeruyours at gmail

Aug 3, 2011, 11:13 PM

Post #6 of 6 (260 views)

Permalink

Thanks a lot. I can make Guest not to reassign my data pages by doing
dma_map_single() on all my data pages.
I will try that.
thanks again.

Regards,
VSR.
On Wed, Aug 3, 2011 at 11:43 PM, Tim Deegan <tim@xen.org> wrote:

> Hi,
>
> At 23:20 +0530 on 03 Aug (1312413612), veerasena reddy wrote:
> > By pinning, I mean to keep the data page always in main memory for the
> > device to access. Once the device processes the page, i can unpin.
> > Please correct me, if i understood page pinning concept wrongly.
> > But, my goal is to keep the page in main memory until the device
> processes
> > it.
>
> If you want to stop _xen_ reassigning this frame (including any
> hypervisor-level paging) you can just take a reference count (probably
> you want a writeable-tyrp typecount using get_page_and_type()). But Xen
> can't stop the guest OS from reusing the frame (including paging its
> contents out), so you will need to address that inside the guest OS.
>
> Tim.
>
> --
> Tim Deegan <tim@xen.org>
> Principal Software Engineer, Xen Platform Team
> Citrix Systems UK Ltd. (Company #02937203, SL9 0BG)
>