Problem:
1) Huge page mapping of anonymous memory is initially invalid. Will be
faulted in by copy-on-write mechanism.
2) Userspace attempts store at the end of the huge mapping.
3) TLB Refill exception handler fill TLB with a normal (4K sized)
invalid page at the end of the huge mapping virtual address range.
4) Userspace restarted, and re-attempts the store at the end of the
huge mapping.
5) Page from #3 is invalid, we get a fault and go to the hugepage
fault handler. This tries to map a huge page and calls
huge_ptep_set_access_flags() to install the mapping.
6) We just call the generic ptep_set_access_flags() to set up the page
tables, but the flush there assumes a normal (4K sized) page and
only tries to flush the first part of the huge page virtual address
out of the TLB, since the existing entry from step #3 doesn't
conflict, nothing is flushed.
7) We attempt to load the mapping into the TLB, but because it
conflicts with the entry from step #3, we get a Machine Check
exception.
The fix: Flush the entire rage covered by the huge page in
huge_ptep_set_access_flags(), and remove the optimization in
local_flush_tlb_range() so that the flush actually does the correct
thing.
Signed-off-by: David Daney <david.daney@cavium.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Cc: Hillf Danton <dhillf@gmail.com>
Patchwork: https://patchwork.linux-mips.org/patch/4661/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
(cherry picked from commit dd617f258cc39d36be26afee9912624a2d23112c)
ac53c4fca4