Re: [Xen-devel] vfree crash

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Petre Ovidiu PIRCALABU <ppircalabu@xxxxxxxxxxxxxxx>
> Sent: 01 July 2019 10:27
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx; 
> Andrew Cooper
> <Andrew.Cooper3@xxxxxxxxxx>
> Cc: Alexandru Stefan ISAILA <aisaila@xxxxxxxxxxxxxxx>; 
> rcojocaru@xxxxxxxxxxxxxxx
> Subject: Re: vfree crash
> 
> On Mon, 2019-07-01 at 08:55 +0000, Paul Durrant wrote:
> > > -----Original Message-----
> > > From: Petre Ovidiu PIRCALABU <ppircalabu@xxxxxxxxxxxxxxx>
> > > Sent: 01 July 2019 09:46
> > > To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>;
> > > xen-devel@xxxxxxxxxxxxxxxxxxxx; Andrew Cooper
> > > <Andrew.Cooper3@xxxxxxxxxx>
> > > Cc: Alexandru Stefan ISAILA <aisaila@xxxxxxxxxxxxxxx>;
> > > rcojocaru@xxxxxxxxxxxxxxx
> > > Subject: Re: vfree crash
> > >
> > > 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.
> >
> > So, looking at the code, I don't think it is intended that
> > v[m|z]alloced pages get assigned to a domain. Could you point at
> > where the assignment is happening?
> >
> >   Paul
> >
> > >
> > > Many thanks,
> > > Petre
> > >
> 
> I'm doing it locally in my test (mock_enable domctl) by calling
> assign_pages for each one allocated by vzalloc.
> 
> https://gitlab.com/xen-project/people/bitdefender/xen/blob/vfree_crash/xen/common/mock.c
> (line 55)

I'm getting a 404 for that URL. But, as Andy says, the problem is that 
assigning to a domain will place the page on a list and that will then mean 
you're gonna have problems calling vfree().

  Paul

> 
> Many thanks,
> Petre

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