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xen-devel
RE: [Xen-devel] [PATCH] iomem: Prevent Dom0 pci bus from allocating RAM
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To: |
Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, "Zhang, Fengzhe" <fengzhe.zhang@xxxxxxxxx>, Jeremy Fitzhardinge <jeremy@xxxxxxxx> |
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Subject: |
RE: [Xen-devel] [PATCH] iomem: Prevent Dom0 pci bus from allocating RAM as I/O space in 2.6.32.27 tree. |
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From: |
"Li, Xin" <xin.li@xxxxxxxxx> |
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Date: |
Thu, 17 Feb 2011 23:07:35 +0800 |
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xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Dong, Eddie" <eddie.dong@xxxxxxxxx>, "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx> |
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Thu, 17 Feb 2011 07:08:14 -0800 |
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Thread-topic: |
[Xen-devel] [PATCH] iomem: Prevent Dom0 pci bus from allocating RAM as I/O space in 2.6.32.27 tree. |
> > However, I still doubt if the igb device is working correctly. The
>
> OK, that is a different bug, if it is a bug.
>
> > sequence that igb driver do ioremap is like this:
> >
> > 1. igb calls function pci_ubs_alloc_resource to get some non-RAM pages.
> > 2. igb sets the phys_addr of the pages in some BAR.
> > 3. igb ioremaps these pages.
> >
> > After patching, it looks like ioremap gets some mfn allocated by
> > Xen. But what set in BAR is still phys_addr. If igb device tries to
>
> No. It just sets the PTE to the PFN.
Then it's just a workaround to the crash. The PFN allocated in dom0 is
actually Xen RAM page, thus the driver may corrupt the page which actually
belongs to Xen or other domain.
>
> > access the pages directly, would Xen be able to intercept and
> > translate it? And also, how the contiguity of mfns be guaranteed?
>
> B/c we don't touch the P2M mapping. We bypass that altogether
> and set the PTE with the phys_addr (which is based on the BARs).
> We can do that since those PFN's belong to the DOMID_IO which
> has a different mechanism for checking the MFN continuity (it
> uses ranges).
I'm still not persuaded this is a reasonable fix. I'm still thinking Xen can't
use the PFN from dom0, it's guest PFN allocated in dom0 according to its e820
which falls into host RAM range.
Thanks!
-Xin
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