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)
The core page allocator ensures that page flags are zeroed when freeing
pages via free_pages_check. A number of architectures (ARM, PPC, MIPS)
rely on this property to treat new pages as dirty with respect to the data
cache and perform the appropriate flushing before mapping the pages into
userspace.
This can lead to cache synchronisation problems when using hugepages,
since the allocator keeps its own pool of pages above the usual page
allocator and does not reset the page flags when freeing a page into the
pool.
This patch adds a new architecture hook, arch_clear_hugepage_flags, so
that architectures which rely on the page flags being in a particular
state for fresh allocations can adjust the flags accordingly when a page
is freed into the pool.
Signed-off-by: Will Deacon <will.deacon@arm.com>
Cc: Michal Hocko <mhocko@suse.cz>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
If we only flush the TLB of the given huge page, the TLB cache remains hot
for the relevant mm as it is, and less will be refilled after flush, huge
or not.
Signed-off-by: Hillf Danton <dhillf@gmail.com>
Cc: linux-mips@linux-mips.org
Acked-by: David Daney <david.daney@cavium.com>
Patchwork: https://patchwork.linux-mips.org/patch/2860/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
