Messages in this thread | | | Subject | Re: [PATCH] xen/gntdev.c: Replace vm_map_pages() with vm_map_pages_zero() | From | Juergen Gross <> | Date | Wed, 31 Jul 2019 08:15:37 +0200 |
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On 30.07.19 20:34, Souptick Joarder wrote: > 'commit df9bde015a72 ("xen/gntdev.c: convert to use vm_map_pages()")' > breaks gntdev driver. If vma->vm_pgoff > 0, vm_map_pages() > will: > - use map->pages starting at vma->vm_pgoff instead of 0 > - verify map->count against vma_pages()+vma->vm_pgoff instead of just > vma_pages(). > > In practice, this breaks using a single gntdev FD for mapping multiple > grants. > > relevant strace output: > [pid 857] ioctl(7, IOCTL_GNTDEV_MAP_GRANT_REF, 0x7ffd3407b6d0) = 0 > [pid 857] mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, 7, 0) = > 0x777f1211b000 > [pid 857] ioctl(7, IOCTL_GNTDEV_SET_UNMAP_NOTIFY, 0x7ffd3407b710) = 0 > [pid 857] ioctl(7, IOCTL_GNTDEV_MAP_GRANT_REF, 0x7ffd3407b6d0) = 0 > [pid 857] mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, 7, > 0x1000) = -1 ENXIO (No such device or address) > > details here: > https://github.com/QubesOS/qubes-issues/issues/5199 > > The reason is -> ( copying Marek's word from discussion) > > vma->vm_pgoff is used as index passed to gntdev_find_map_index. It's > basically using this parameter for "which grant reference to map". > map struct returned by gntdev_find_map_index() describes just the pages > to be mapped. Specifically map->pages[0] should be mapped at > vma->vm_start, not vma->vm_start+vma->vm_pgoff*PAGE_SIZE. > > When trying to map grant with index (aka vma->vm_pgoff) > 1, > __vm_map_pages() will refuse to map it because it will expect map->count > to be at least vma_pages(vma)+vma->vm_pgoff, while it is exactly > vma_pages(vma). > > Converting vm_map_pages() to use vm_map_pages_zero() will fix the > problem. > > Marek has tested and confirmed the same. > > Reported-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com> > Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com> > Tested-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Pushed to xen/tip.git for-linus-5.3a
Juergen
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