[Xen-devel] RE: /dev/mem and /dev/kmem

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

>From: Keir Fraser [mailto:Keir.Fraser@xxxxxxxxxxxx]
>Sent: 2007年3月22日 0:33
>
>On 21/3/07 12:35, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:
>
>> So how about applications which simply use /dev/mem to map
>> normal domain memory? Seems this breaks compatibility
>> in user level though desired for above Xserver case... Or such
>> case is rare?
>
>This case seems not to occur in practise (no complaints so far and our
>/dev/mem has had this limitation since day one). This is perhaps not
>surprising: really not much good can come out of direct grokking of
>kernel-maintained memory without the kernel's knowledge.
>
>> BTW, I didn't find code to protect Xen to be mapped in this path,
>> like in get_page_from_l1e(). Could you help pointing out?
>
>Not sure how you mean. Only pages that explicitly are owned by a
>domain and
>have a non-zero refcount can have get_page() succeed on them. So
>random
>Xen-owned pages are safe.
>
> -- Keir

I just wanted to know how to prevent dom0 from mapping 
xen-owned pages. You're right and I missed the get_page() point here. :-)

Thanks,
Kevin

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