When a page fault happens in a GPU, the GPU signals the OS and the GPU
driver calls the fault handler which populated a page table; this allows
the GPU to complete an ATS request.
On the bare metal get_user_pages() is enough as it adds a pte to
the kernel page table but under KVM the partition scope tree does not get
updated so ATS will still fail.
This reads a byte from an effective address which causes HV storage
interrupt and KVM updates the partition scope tree.
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
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