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From: Peter Maydell <peter.maydell@linaro.org>
Date: Tue, 3 Dec 2013 20:59:52 +0000
Message-ID: <CAFEAcA96tROoh2UdgTXPkowzbxRzZ4tdyVSWVQrjEA1tw2abMA@mail.gmail.com>
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Subject: Re: [Qemu-devel] [PATCH 07/23] hw/pci/pcie_aer.c: fix buffer
 overruns on invalid state load
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: QEMU Developers <qemu-devel@nongnu.org>, Anthony Liguori <anthony@codemonkey.ws>, qemu-stable <qemu-stable@nongnu.org>

On 3 December 2013 20:41, Michael S. Tsirkin <mst@redhat.com> wrote:
> On Tue, Dec 03, 2013 at 06:30:46PM +0000, Peter Maydell wrote:
>> On 3 December 2013 16:28, Michael S. Tsirkin <mst@redhat.com> wrote:
>> >  const VMStateDescription vmstate_pcie_aer_log = {
>> >      .name = "PCIE_AER_ERROR_LOG",
>> >      .version_id = 1,
>> >      .minimum_version_id = 1,
>> >      .minimum_version_id_old = 1,
>> > +    .post_load = pcie_aer_state_post_load,
>> >      .fields     = (VMStateField[]) {
>> >          VMSTATE_UINT16(log_num, PCIEAERLog),
>> > -        VMSTATE_UINT16(log_max, PCIEAERLog),
>> > -        VMSTATE_STRUCT_VARRAY_POINTER_UINT16(log, PCIEAERLog, log_num,
>> > +        VMSTATE_UINT16_EQUAL(log_max, PCIEAERLog),
>> > +        VMSTATE_STRUCT_VARRAY_POINTER_UINT16(log, PCIEAERLog, log_max,
>> >                                vmstate_pcie_aer_err, PCIEAERErr),
>> >          VMSTATE_END_OF_LIST()
>> >      }
>>
>> Isn't this a migration compability break?
>
> How is it a break?

If a QEMU with this patch sends data to a QEMU without it, then the
receiving end will think it should expect log_num array entries but the
sending end is going to send log_max of them. Conversely, an old->new
migration is going to send fewer array entries than the destination
expects. Or have I misinterpreted how the VARRAY entries work?

thanks
-- PMM