Re: [Xen-devel] [PATCH 2/2] xen/privcmd: add PRIVCMD_MMAPBATCH_V2 ioctl

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2012-08-30 at 19:29 +0100, Andres Lagar-Cavilla wrote:
> On Aug 30, 2012, at 1:04 PM, David Vrabel wrote:
> > You can't access user space pages here while holding
> > current->mm->mmap_sem.  I tried this and it would sometimes deadlock in
> > the page fault handler.
> > 
> > access_ok() only checks if the pointer is in the user space virtual
> > address space - not that a valid mapping exists and is writable.  So
> > BUG_ON(__put_user()) should not be done.
> 
> Very true. Thanks for the pointer. Clearly the reason for the 
> gather_array/traverse_pages structure.

/me has flashbacks to the mammoth debugging session which led to
http://xenbits.xen.org/hg/linux-2.6.18-xen.hg/rev/043dc7488c11.

Ian.



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel