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[Xen-devel] update_va_mapping_otherdomain

To: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] update_va_mapping_otherdomain
From: "Michael R. Hines" <mhines@xxxxxxxxxxxxxxxxx>
Date: Fri, 07 Sep 2007 21:29:23 -0400
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I have a technical question about update_va_mapping_otherdomain.......

I have two components: a C program linked against libxc
and a kernel module which performs the following simple
sequence of events from domain zero:

1. Pause guest (unprivileged)
2. Grabs the PTE associated with a random (but present) page
   within the guest's kernel's address space
   (using a modified xc_translate_foreign_address)
3. Flips the present bit to zero
4. Calls HYPERVISOR_update_va_mapping otherdomain (from the kernel module)
5. Re-performs xc_translate_foreign_address on the same PTE
6. Verifies the the present bit was indeed changed to zero

Upon successful return from update_va_mapping (i.e. return code == zero),
my problem involves the last step mentioned above. The present bit still
remains unchanged (is still one), although update_va_mapping return true.

What might cause such a strange problem to occur?

Michael R. Hines
Live long and prosper...

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