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[Xen-devel] query the page type of a hvm page from within a hvm guest

To: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] query the page type of a hvm page from within a hvm guest
From: Olaf Hering <olaf@xxxxxxxxx>
Date: Thu, 7 Apr 2011 12:12:02 +0200
Delivery-date: Thu, 07 Apr 2011 03:12:45 -0700
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Now that kdump works with pv-on-hvm guests, one issue remains:
The balloon driver in the guest frees guest pages and marks them as
mmio. When the kernel crashes and the crash kernel attempts to read the
oldmem via /proc/vmcore a read from ballooned pages will generate 100%
load in dom0 because Xen asks qemu-dm for the page content. Since the
reads come in as 8byte requests each ballooned page is tried 512 times.

If the crash kernel had a way to ask the hypervisor wether a specific
guest gfn is ballooned and thus backed by ram, the load issue would not
happen.  There seems to be no interface to query the type of a guest gfn
from within the hvm guest.

Any ideas how to implement that?
I see HVMOP_set_mem_type, but no HVMOP_get_mem_type.


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