From mboxrd@z Thu Jan  1 00:00:00 1970
From: bugzilla-daemon@bugzilla.kernel.org
Subject: [Bug 53611] New: nVMX: Add nested EPT
Date: Mon, 11 Feb 2013 12:49:06 +0000 (UTC)
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https://bugzilla.kernel.org/show_bug.cgi?id=53611

           Summary: nVMX: Add nested EPT
           Product: Virtualization
           Version: unspecified
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: kvm
        AssignedTo: virtualization_kvm@kernel-bugs.osdl.org
        ReportedBy: nyh@math.technion.ac.il
        Regression: No


Created an attachment (id=93101)
 --> (https://bugzilla.kernel.org/attachment.cgi?id=93101)
Nested EPT patches, v2

Nested EPT means emulating EPT for an L1 guest, allowing it to use EPT when
running a nested guest L2. When L1 uses EPT, it allows the L2 guest to set
its own cr3 and take its own page faults without either of L0 or L1 getting
involved. In many workloads this significanlty improves L2's performance over
the previous two alternatives (shadow page tables over ept, and shadow page
tables over shadow page tables). As an example, I measured a single-threaded
"make", which has a lot of context switches and page faults, on the three
options:

 shadow over shadow: 105 seconds
 shadow over EPT: 87 seconds      (this is the default currently)
 EPT over EPT: 29 seconds

 single-level virtualization (with EPT): 25 seconds

So clearly nested EPT would be a big win for such workloads.

I attach a patch set which I worked on and allowed me to measure the above
results. This is the same patch set I sent to KVM mailing list on August 1st,
2012, titled "nEPT v2: Nested EPT support for Nested VMX".

This patch set still needs some work: it is known to only work in some setups
but not others, and the file "announce" in the attached tar lists 5 things
which definitely need to be done. There were a few additional comments in the
mailing list - see
http://comments.gmane.org/gmane.comp.emulators.kvm.devel/95395

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