On Fri, 9 Sep 2022, Juergen Gross wrote:
On 09.09.22 04:11, Stefano Stabellini wrote:
Adding more people in CC
On Thu, 8 Sep 2022, Stefano Stabellini wrote:
Hi Juergen,
A colleague is seeing a failure on x86 in Linux Dom0. The failure is
pin_user_pages_fast with addresses that correspond to foreign memory
pages:
- QEMU maps a domU address using dma_memory_map (xen_map_cache)
- QEMU calls an IOCTL to the TEE subsystem with the Virtual Address
returned by dma_memory_map
- Linux tee_shm_register->pin_user_pages_fast Returns -14 -
drivers/tee/tee_shm.c
Once upon a time it used to be the case that get_user_pages_fast would
fail on Xen because we didn't have a struct page corresponding to
foreign memory mappings. But that hasn't been the case for years now.
Any other ideas why it would fail?
I think we can expect that access_ok() isn't failing.
I assume the mapping was done allowing writes (sorry for paranoia mode)?
I was told it was verified: QEMU could read and write to the VA returned
by dma_memory_map. From /proc/<qemu-pid>/maps, the VA assigned after the
mapping is pointing to /dev/xen/privcmd.
Other than that I'm not having enough memory management skills. It might be
related to mmap()-ed foreign pages having _PAGE_SPECIAL set, though.
Do we still set PAGE_SPECIAL for foreign mapped pages? It looks like it
is not there anymore? If PAGE_SPECIAL is not there, then they really
should look like regular pages?
