powerpc/64s/radix: Fix MADV_[FREE|DONTNEED] TLB flush miss problem with THP

The patch 99baac21e4 ("mm: fix MADV_[FREE|DONTNEED] TLB flush miss
problem") added a force flush mode to the mmu_gather flush, which
unconditionally flushes the entire address range being invalidated
(even if actual ptes only covered a smaller range), to solve a problem
with concurrent threads invalidating the same PTEs causing them to
miss TLBs that need flushing.

This does not work with powerpc that invalidates mmu_gather batches
according to page size. Have powerpc flush all possible page sizes in
the range if it encounters this concurrency condition.

Patch 4647706ebe ("mm: always flush VMA ranges affected by
zap_page_range") does add a TLB flush for all page sizes on powerpc for
the zap_page_range case, but that is to be removed and replaced with
the mmu_gather flush to avoid redundant flushing. It is also thought to
not cover other obscure race conditions:

https://lkml.kernel.org/r/[email protected]

Hash does not have a problem because it invalidates TLBs inside the
page table locks.

Reported-by: Aneesh Kumar K.V <[email protected]>
Signed-off-by: Nicholas Piggin <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>

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