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Re: [Qemu-devel] [Xen-devel] virtio leaks cpu mappings, was: qemu crash
From: |
Jason Wang |
Subject: |
Re: [Qemu-devel] [Xen-devel] virtio leaks cpu mappings, was: qemu crash with virtio on Xen domUs (backtrace included) |
Date: |
Wed, 26 Nov 2014 13:23:50 +0800 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 |
On 11/25/2014 09:53 PM, Stefano Stabellini wrote:
> On Tue, 25 Nov 2014, Jason Wang wrote:
>> On 11/25/2014 02:44 AM, Stefano Stabellini wrote:
>>> On Mon, 24 Nov 2014, Stefano Stabellini wrote:
>>>> On Mon, 24 Nov 2014, Stefano Stabellini wrote:
>>>>> CC'ing Paolo.
>>>>>
>>>>>
>>>>> Wen,
>>>>> thanks for the logs.
>>>>>
>>>>> I investigated a little bit and it seems to me that the bug occurs when
>>>>> QEMU tries to unmap only a portion of a memory region previously mapped.
>>>>> That doesn't work with xen-mapcache.
>>>>>
>>>>> See these logs for example:
>>>>>
>>>>> DEBUG address_space_map phys_addr=78ed8b44 vaddr=7fab50afbb68 len=0xa
>>>>> DEBUG address_space_unmap vaddr=7fab50afbb68 len=0x6
>>>> Sorry the logs don't quite match, it was supposed to be:
>>>>
>>>> DEBUG address_space_map phys_addr=78ed8b44 vaddr=7fab50afbb64 len=0xa
>>>> DEBUG address_space_unmap vaddr=7fab50afbb68 len=0x6
>>> It looks like the problem is caused by iov_discard_front, called by
>>> virtio_net_handle_ctrl. By changing iov_base after the sg has already
>>> been mapped (cpu_physical_memory_map), it causes a leak in the mapping
>>> because the corresponding cpu_physical_memory_unmap will only unmap a
>>> portion of the original sg. On Xen the problem is worse because
>>> xen-mapcache aborts.
>>>
>>> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
>>> index 2ac6ce5..b2b5c2d 100644
>>> --- a/hw/net/virtio-net.c
>>> +++ b/hw/net/virtio-net.c
>>> @@ -775,7 +775,7 @@ static void virtio_net_handle_ctrl(VirtIODevice *vdev,
>>> VirtQueue *vq)
>>> struct iovec *iov;
>>> unsigned int iov_cnt;
>>>
>>> - while (virtqueue_pop(vq, &elem)) {
>>> + while (virtqueue_pop_nomap(vq, &elem)) {
>>> if (iov_size(elem.in_sg, elem.in_num) < sizeof(status) ||
>>> iov_size(elem.out_sg, elem.out_num) < sizeof(ctrl)) {
>>> error_report("virtio-net ctrl missing headers");
>>> @@ -784,8 +784,12 @@ static void virtio_net_handle_ctrl(VirtIODevice *vdev,
>>> VirtQueue *vq)
>>>
>>> iov = elem.out_sg;
>>> iov_cnt = elem.out_num;
>>> - s = iov_to_buf(iov, iov_cnt, 0, &ctrl, sizeof(ctrl));
>>> iov_discard_front(&iov, &iov_cnt, sizeof(ctrl));
>>> +
>>> + virtqueue_map_sg(elem.in_sg, elem.in_addr, elem.in_num, 1);
>>> + virtqueue_map_sg(elem.out_sg, elem.out_addr, elem.out_num, 0);
>>> +
>>> + s = iov_to_buf(iov, iov_cnt, 0, &ctrl, sizeof(ctrl));
>> Does this really work?
> It seems to work here, as in it doesn't crash QEMU and I am able to boot
> a guest with network. I didn't try any MAC related commands.
>
It was because the guest (not a recent kernel?) never issue commands
through control vq.
We'd better hide the implementation details such as virtqueue_map_sg()
in virtio core instead of letting device call it directly.
>> The code in fact skips the location that contains
>> virtio_net_ctrl_hdr. And virtio_net_handle_mac() still calls
>> iov_discard_front().
>>
>> How about copy iov to a temp variable and use it in this function?
> That would only work if I moved the cpu_physical_memory_unmap call
> outside of virtqueue_fill, so that we can pass different iov to them.
> We need to unmap the same iov that was previously mapped by
> virtqueue_pop.
>
I mean something like following or just passing the offset of iov to
virtio_net_handle_*().
diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 9b88775..fdb4edd 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -798,7 +798,7 @@ static void virtio_net_handle_ctrl(VirtIODevice
*vdev, VirtQueue *vq)
virtio_net_ctrl_ack status = VIRTIO_NET_ERR;
VirtQueueElement elem;
size_t s;
- struct iovec *iov;
+ struct iovec *iov, *iov2;
unsigned int iov_cnt;
while (virtqueue_pop(vq, &elem)) {
@@ -808,8 +808,12 @@ static void virtio_net_handle_ctrl(VirtIODevice
*vdev, VirtQueue *vq)
exit(1);
}
- iov = elem.out_sg;
iov_cnt = elem.out_num;
+ s = sizeof(struct iovec) * elem.out_num;
+ iov = g_malloc(s);
+ memcpy(iov, elem.out_sg, s);
+ iov2 = iov;
+
s = iov_to_buf(iov, iov_cnt, 0, &ctrl, sizeof(ctrl));
iov_discard_front(&iov, &iov_cnt, sizeof(ctrl));
if (s != sizeof(ctrl)) {
@@ -833,6 +837,7 @@ static void virtio_net_handle_ctrl(VirtIODevice
*vdev, VirtQueue *vq)
virtqueue_push(vq, &elem, sizeof(status));
virtio_notify(vdev, vq);
+ g_free(iov2);
}
}
- [Qemu-devel] qemu crash with virtio on Xen domUs (backtrace included), Fabio Fantoni, 2014/11/24
- Re: [Qemu-devel] qemu crash with virtio on Xen domUs (backtrace included), Wen Congyang, 2014/11/24
- Re: [Qemu-devel] qemu crash with virtio on Xen domUs (backtrace included), Stefano Stabellini, 2014/11/24
- Re: [Qemu-devel] [Xen-devel] qemu crash with virtio on Xen domUs (backtrace included), Stefano Stabellini, 2014/11/24
- [Qemu-devel] virtio leaks cpu mappings, was: qemu crash with virtio on Xen domUs (backtrace included), Stefano Stabellini, 2014/11/24
- Re: [Qemu-devel] [Xen-devel] virtio leaks cpu mappings, was: qemu crash with virtio on Xen domUs (backtrace included), Konrad Rzeszutek Wilk, 2014/11/24
- Re: [Qemu-devel] [Xen-devel] virtio leaks cpu mappings, was: qemu crash with virtio on Xen domUs (backtrace included), Stefano Stabellini, 2014/11/24
- Re: [Qemu-devel] virtio leaks cpu mappings, was: qemu crash with virtio on Xen domUs (backtrace included), Wen Congyang, 2014/11/24
- Re: [Qemu-devel] [Xen-devel] virtio leaks cpu mappings, was: qemu crash with virtio on Xen domUs (backtrace included), Jason Wang, 2014/11/25
- Re: [Qemu-devel] [Xen-devel] virtio leaks cpu mappings, was: qemu crash with virtio on Xen domUs (backtrace included), Stefano Stabellini, 2014/11/25
- Re: [Qemu-devel] [Xen-devel] virtio leaks cpu mappings, was: qemu crash with virtio on Xen domUs (backtrace included),
Jason Wang <=
- Re: [Qemu-devel] [Xen-devel] virtio leaks cpu mappings, was: qemu crash with virtio on Xen domUs (backtrace included), Stefano Stabellini, 2014/11/26
- Re: [Qemu-devel] [Xen-devel] virtio leaks cpu mappings, was: qemu crash with virtio on Xen domUs (backtrace included), Jason Wang, 2014/11/27