Re: MULTI_mmu_update, HYPERVISOR_mmu_update and pte entry

[Christopher Benninger <chrisbenninger@gmail.com>]

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Hi Jeremy,

I am definitely doing something weird, but on purpose. I am trying to
determine which process specifically owns the pte in question. I have a domU
module which I can ask for information, I just dont know how to get the ptr
provided, into a useful context I can send it.

Chris Benninger

University of Victoria, Computer Science
cbenning@cs.uvic.ca
http://benninger.ca



On Tue, May 17, 2011 at 10:29 PM, Jeremy Fitzhardinge <jeremy@goop.org>wrote:

> On 05/12/2011 03:41 PM, chrisbenninger wrote:
> > Hi, I am working on being able to determine which process owns a PTE
> > being changed during each MMU update in 64-bit paravirtualized mode. I
> > have a couple questions here.
> >
> > 1. When a linux DomU wants to make an update to a PTE, it calls
> > HYPERVISOR_mmu_update? In my case it appears to be calling
> > MULTI_mmu_update mostly. Are these two functions the only primary ways
> > a VM will ask for an MMU update?
>
> There's also update_va_mapping and direct writes to the pte which are
> trapped and emulated.  However, I've got patches to drop the use of
> update_va_mapping in pvops Linux, at least.
>
> > 2. The mmu_update struct that comes along with a MMU update has a
> > /unint64_t ptr/  which is a machine address to the PTE being changed.
> > Is there any way to use this machine address and determine the pte_t
> > or page from within a DomU?
>
> From within domU?  You could convert it back into a pseudo-phys address
> and get the pfn, but its hard to connect a random pte page to a virtual
> address or even connect it to an address space.
>
> What are you trying to achieve?  Most usermode pte updates will be to
> the current process.
>
>    J
>

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