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[Xen-ia64-devel] RE: how to put kernel module in xen/ipf

To: "Magenheimer, Dan \(HP Labs Fort Collins\)" <dan.magenheimer@xxxxxx>
Subject: [Xen-ia64-devel] RE: how to put kernel module in xen/ipf
From: "Xu, Anthony" <anthony.xu@xxxxxxxxx>
Date: Wed, 22 Jun 2005 09:57:25 +0800
Cc: xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
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Thread-topic: how to put kernel module in xen/ipf

Hi, Dan,


We implemented VTLB infrastructure per domain on XEN/IPF, which tracked guest tlb information. VTLB has fixed size, then when using out of it, HV will desert all VTLB and recycle VTLB. We add a flag “lock” in VTLB entry, when HV recycle VTLB, the VTLB entry with “lock” flag will not be deserted, but if Guest uses instructions like “ptc” to purge tlb, the VTLB entry with “lock” flag will be deserted.


Before invoking hypercall,

Kernel Module pseudo read parameter once per page size to make sure the translation for this parameter has been inserted in VTLB infrastructure. Then kernel Module will call another new hypercall which don’t need pointer parameter to lock above translation in VTLB infrastructure.


Then invoking this hypercall,

In HV, HV will use copy_from_user() or copy_to_user() to get parameter or return result. In these functions, HV will lookup VTLB infrastructure to get corresponding guest physical address of the parameter, because this translation has been locked in VTLB, HV definitely can find it, then HV can get corresponding machine address from physical to machine address table, as we know HV use region 7 for identity mapping, HV can get identity virtual address for that machine address, at last, HV do normal copy operation using this identity virtual address.


After this hypercall,

Guest application definitely will unmap the memory allocated for passing hypercall parameter, and this operation definitely will purge tlb for this address, so the “lock” VTLB entry in VTLB infrastructure can be recycled.


We had tested this parameter passing mechanism for several hypercalls, such as GETMEMLIST, and it works well.


Could we check in this patch and discuss further?






From: Magenheimer, Dan (HP Labs Fort Collins) [mailto:dan.magenheimer@xxxxxx]
Sent: 2005
621 22:04
To: Xu, Anthony
Cc: xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
Subject: RE: how to put kernel module in xen/ipf


Yes, the hypercall parameter mechanism is still evolving for Xen/ia64.  Very few

hypercalls are necessary to run domain0, so experimentation with different hypercall

mechanisms has waited until multi-domain work.


Can you explain more about kernel modules?  I know (roughly) how they

work for Linux, but not how they are used on Xen/x86.  Others on this

list might like to learn too, so perhaps you could explain the design

in detail?



From: Xu, Anthony [mailto:anthony.xu@xxxxxxxxx]
Sent: Monday, June 20, 2005 11:10 PM
To: Magenheimer, Dan (HP Labs Fort Collins)
Cc: xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
Subject: how to put kernel module in xen/ipf

Hi, Dan,       

XEN/IPF kernel module has a lot of difference from XEN/ia32, especially the mechanism of passing hypercall parameter. Currently we create directory “km” under xen/arch/ia64, and put kernel module code in that directory.

        Any comment?


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