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Re: [Xen-devel] MULTI_mmu_update, HYPERVISOR_mmu_update and pte entry

  • To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
  • From: Christopher Benninger <chrisbenninger@xxxxxxxxx>
  • Date: Wed, 18 May 2011 05:25:30 +0000
  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Tue, 17 May 2011 22:26:37 -0700
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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

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


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