[Bug 67061] New: [Nested]L2 guest boot up fail(kvm on kvm).

[Bug 67061] New: [Nested]L2 guest boot up fail(kvm on kvm).

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=67061

            Bug ID: 67061
           Summary: [Nested]L2 guest boot up fail(kvm on kvm).
           Product: Virtualization
           Version: unspecified
    Kernel Version: 3.13.0-rc1
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: kvm
          Assignee: virtualization_kvm@kernel-bugs.osdl.org
          Reporter: chao.zhou@intel.com
        Regression: No

Environment:
------------
Host OS (ia32/ia32e/IA64):ia32e
Guest OS (ia32/ia32e/IA64):ia32e
Guest OS Type (Linux/Windows):Linux
kvm.git Commit:2ecd1aba597726c9053ba1a112e3d8fdc5ca08ff
qemu-kvm Commit:5c5432e7d630592ddcc1876ac8a1505f8f14ef15
Host Kernel Version:3.12.0
Hardware:Romley_EP


Bug detailed description:
--------------------------
when create L2 guest, the L2 guest boot up fail.
note:
1. L1 guest is kvm on kvm.
2. This should be a kernel bug
kvm      + qemu     =  result
f0804804 + 5c5432e7 = bad
ede58222 + 5c5432e7 = good

Reproduce steps:
----------------
1.create L1 guest:
qemu-system-x86_64 -enable-kvm -m 6G -smp 4 -net nic,macaddr=00:12:52:13:46:67
-net tap,script=/etc/kvm/qemu-ifup ia32e_nested_kvm.img -cpu host
2.create L2 guest:
qemu-system-x86_64 -enable-kvm -m 1G -smp 2 -net none ia32e_rhel6u4.img

Current result:
----------------
L2 guest boot  up fail
Expected result:
----------------
after create L2 guest, L2 guest works fine

Basic root-causing log:
----------------------

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[Bug 67061] [Nested]L2 guest boot up fail(kvm on kvm).

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=67061

--- Comment #1 from Zhou, Chao <chao.zhou@intel.com> ---
the first bad commit is:
commit 8a29111c7ca68d928dfab58636f3f6acf0ac04f7
Author: Eric Dumazet <edumazet@google.com>
Date:   Tue Oct 8 09:02:23 2013 -0700

    net: gro: allow to build full sized skb

    skb_gro_receive() is currently limited to 16 or 17 MSS per GRO skb,
    typically 24616 bytes, because it fills up to MAX_SKB_FRAGS frags.

    It's relatively easy to extend the skb using frag_list to allow
    more frags to be appended into the last sk_buff.

    This still builds very efficient skbs, and allows reaching 45 MSS per
    skb.

    (45 MSS GRO packet uses one skb plus a frag_list containing 2 additional
    sk_buff)

    High speed TCP flows benefit from this extension by lowering TCP stack
    cpu usage (less packets stored in receive queue, less ACK packets
    processed)

    Forwarding setups could be hurt, as such skbs will need to be
    linearized, although its not a new problem, as GRO could already
    provide skbs with a frag_list.

    We could make the 65536 bytes threshold a tunable to mitigate this.

    (First time we need to linearize skb in skb_needs_linearize(), we could
    lower the tunable to ~16*1460 so that following skb_gro_receive() calls
    build smaller skbs)

    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>

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[Bug 67061] [BISECTED][Nested]L2 guest boot up fail(kvm on kvm).

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=67061

Alan <alan@lxorguk.ukuu.org.uk> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |alan@lxorguk.ukuu.org.uk
            Summary|[Nested]L2 guest boot up    |[BISECTED][Nested]L2 guest
                   |fail(kvm on kvm).           |boot up fail(kvm on kvm).

--- Comment #2 from Alan <alan@lxorguk.ukuu.org.uk> ---
Thats a very odd bisection point it must be said

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[Bug 67061] [BISECTED][Nested]L2 guest boot up fail(kvm on kvm).

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=67061

Thilo Fromm <kontakt@thilo-fromm.de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |kontakt@thilo-fromm.de

--- Comment #3 from Thilo Fromm <kontakt@thilo-fromm.de> ---
This bug may have been fixed in 3.13.6.

I was affected by this bug, too - I use nested virtualization a lot, mainly for
system testing purposes. I was able to reproduce the issue on all 3.13 kernels
so far; my hardware is a Intel Core i7-2640M.

Kernel release 3.13.6 fixed the issue for me. Looking at the changelog at
https://www.kernel.org/pub/linux/kernel/v3.x/ChangeLog-3.13.6, I guess the fix
was in commit 92cb6f3c5533832aa70a7dc9326ef21270169583 " kvm, vmx: Really fix
lazy FPU on nested guest".

The issue is discussed on the kvm-devel mailing list:
http://thread.gmane.org/gmane.comp.emulators.kvm.devel/119328 leading to the
fix: http://permalink.gmane.org/gmane.linux.kernel.stable/82043.

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[Bug 67061] [BISECTED][Nested]L2 guest boot up fail(kvm on kvm).

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=67061

Paolo Bonzini <bonzini@gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |bonzini@gnu.org
         Resolution|---                         |CODE_FIX

--- Comment #4 from Paolo Bonzini <bonzini@gnu.org> ---
I agree with the explanation in comment 3.

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