Re: [Xen-devel] [PATCH v1 7/8]: PVH privcmd changes

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

On Wed, 3 Oct 2012 14:21:35 +0100
Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:

> On Fri, 2012-09-21 at 20:21 +0100, Mukesh Rathor wrote:
> > +static int pvh_privcmd_resv_pfns(struct vm_area_struct *vma, int
> > numpgs)
> ...
> > +       pvhp->pi_num_pgs = numpgs;
> > +       BUG_ON(vma->vm_private_data != (void *)1);
> > +       vma->vm_private_data = pvhp; 
> 
> How does this interact with:
> 
> static int privcmd_enforce_singleshot_mapping(struct vm_area_struct
> *vma) {
>       return (xchg(&vma->vm_private_data, (void *)1) == NULL);
> }
> 
> If someone tries to map a second time then won't this correct the pvhp
> in vm_private_data by resetting it to 1? Then when the original
> mapping is torn down things all fall apart?
> 
> Perhaps we need a cmpxchg here? Or to rework the callers a little bit
> perhaps.

Right, that's why I had it originally checking for auto xlated and
doing something different. I think that is better than to change this
and change again. I'll change it back to just putting the ptr here.


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