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Re: [Xen-devel] vfree crash
- To: Petre Ovidiu PIRCALABU <ppircalabu@xxxxxxxxxxxxxxx>, Paul Durrant <Paul.Durrant@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Mon, 1 Jul 2019 09:56:18 +0100
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- Cc: Alexandru Stefan ISAILA <aisaila@xxxxxxxxxxxxxxx>, "rcojocaru@xxxxxxxxxxxxxxx" <rcojocaru@xxxxxxxxxxxxxxx>
- Delivery-date: Mon, 01 Jul 2019 08:56:31 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 01/07/2019 09:45, Petre Ovidiu PIRCALABU wrote:
> On Mon, 2019-07-01 at 08:29 +0000, Paul Durrant wrote:
>>> -----Original Message-----
>>> From: Xen-devel <xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx> On Behalf
>>> Of Petre Ovidiu PIRCALABU
>>> Sent: 28 June 2019 19:00
>>> To: xen-devel@xxxxxxxxxxxxxxxxxxxx; Andrew Cooper <
>>> Andrew.Cooper3@xxxxxxxxxx>
>>> Cc: Alexandru Stefan ISAILA <aisaila@xxxxxxxxxxxxxxx>;
>>> rcojocaru@xxxxxxxxxxxxxxx
>>> Subject: [Xen-devel] vfree crash
>>>
>>> Hello,
>>>
>>> I need your help to pinpoint the root cause of a problem. To my
>>> understanding vfree should be used when allocating memory with
>>> vmalloc.
>>>
>>> But, I have the following scenario which results in a XEN crash:
>>> - allocate a number of frames using vmalloc (vzalloc) (e.g. using a
>>> domctl) and assign them to the calling domain
>>> - map the frames using xenforeignmemory_map_resource
>> Do you really mean xenforeignmemory_map_resource()? If the memory is
>> assigned to the calling domain then this is quite likely not to work.
>> There were reference counting problems with that code, which is why
>> caller assigned resources were dropped.
>>
>> Paul
>>
> The problem lies with vfree because it creates a new list with the
> pages, unmaps the va pointer and then frees the pages. If I do these
> steps manually (without adding them to a new list) it works.
The problem here is that struct page_info only has a single linked list
pointer, and vfree() blindly assumes it is available for use, which
isn't true once you've called assign_pages() on the vmap area.
At the moment, it doesn't look like it is possible to set v*alloc()'d
pages up suitably to be mapped by a guest. (Similar corruption will
occur via share_xen_page_with_guest() and the xenheap list).
This is obviously something which wants fixing, but its not immediately
obvious how.
~Andrew
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