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Re: [Xen-devel] Question about PV guest accessing /dev/mem

To: "Oehrlein, Scott" <scott.oehrlein@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Question about PV guest accessing /dev/mem
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Wed, 28 Jul 2010 07:49:14 +0100
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On 28/07/2010 02:37, "Oehrlein, Scott" <scott.oehrlein@xxxxxxxxx> wrote:

> I can then read/write to the devices config space using logicaladdress. When
> using Xen¹s PV functionality with pciback/pcifront to assign the device to the
> guest on a platform without VT-d support, an attempt to use logicaladdress
> results in the following error in ``xm dmesg¹¹:
>  
> (XEN) mm.c:1747:d23 Bad L1 flags 800000
>  
> Does this mean Xen¹s mmu is not mapping gfn to mfn correctly? Or what is
> happening after the call to mmap that is different from native path?

I think that means the guest OS is trying to map a PTE with the NX bit set
when your processor does not support NX. Xen disallows that, and it would be
a bug in the guest (Linux 2.6.34 in this case?).

 -- Keir




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