The nest MMU in POWER9 does not re-fetch the PTE in response to
permission mismatch, contrary to the architecture[*] and unlike the core
MMU. This requires a TLB flush before upgrading permissions of valid
PTEs, for any address space with a coprocessor attached.
Per (non-public) Nest MMU Workbook, POWER10 nest MMU conforms to the
architecture in this regard, so skip the workaround.
[*] See: Power ISA Version 3.1B, 6.10.1.2 Modifying a Translation Table
Entry, Setting a Reference or Change Bit or Upgrading Access
Authority (PTE Subject to Atomic Hardware Updates):
"If the only change being made to a valid PTE that is subject to
atomic hardware updates is to set the Reference or Change bit to
1 or to upgrade access authority, a simpler sequence suffices
because the translation hardware will refetch the PTE if an
access is attempted for which the only problems were reference
and/or change bits needing to be set or insufficient access
authority."
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220525022358.780745-3-npiggin@gmail.com
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