Random memory corruption may occur due to incorrent tlb flushes

Hi Greg/Sasha,

The commit a46cc7a90fd (powerpc/mm/radix: Improve TLB/PWC flushes) picked up in 4.14 release has the potential to cause random memory corruption. This was fixed in 5.5 by the following patches.

12e4d53f3f powerpc/mmu_gather: enable RCU_TABLE_FREE even for !SMP case 0ed1325967 mm/mmu_gather: invalidate TLB correctly on batch allocation failure and flush 0758cd8304 asm-generic/tlb: avoid potential double flush

It's a bit tricky to backport to 4.14 stable (though I have a backport to 4.19 stable, which I will post shortly). If you think it's important to fix this in 4.14, it would easier to revert the above mentioned commit (a46cc7a90fd).

Please let me know your thoughts.

Thanks, Santosh