Re: Linux pin_user_pages_fast fails on Xen

[Juergen Gross]

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)?

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.


Juergen

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