diff options
author | Dave Hansen <dave.hansen@linux.intel.com> | 2016-07-07 17:19:14 -0700 |
---|---|---|
committer | Ingo Molnar <mingo@kernel.org> | 2016-07-13 09:43:25 +0200 |
commit | e4a84be6f05eab4778732d799f63b3cd15427885 (patch) | |
tree | 7b5c31fb9264f7daf0b66284a2392bb46e11e321 /crypto/cmac.c | |
parent | 97e3c602ccbdd7db54e92fe05675c664c052a466 (diff) | |
download | linux-e4a84be6f05eab4778732d799f63b3cd15427885.tar.bz2 |
x86/mm: Disallow running with 32-bit PTEs to work around erratum
The Intel(R) Xeon Phi(TM) Processor x200 Family (codename: Knights
Landing) has an erratum where a processor thread setting the Accessed
or Dirty bits may not do so atomically against its checks for the
Present bit. This may cause a thread (which is about to page fault)
to set A and/or D, even though the Present bit had already been
atomically cleared.
These bits are truly "stray". In the case of the Dirty bit, the
thread associated with the stray set was *not* allowed to write to
the page. This means that we do not have to launder the bit(s); we
can simply ignore them.
If the PTE is used for storing a swap index or a NUMA migration index,
the A bit could be misinterpreted as part of the swap type. The stray
bits being set cause a software-cleared PTE to be interpreted as a
swap entry. In some cases (like when the swap index ends up being
for a non-existent swapfile), the kernel detects the stray value
and WARN()s about it, but there is no guarantee that the kernel can
always detect it.
When we have 64-bit PTEs (64-bit mode or 32-bit PAE), we were able
to move the swap PTE format around to avoid these troublesome bits.
But, 32-bit non-PAE is tight on bits. So, disallow it from running
on this hardware. I can't imagine anyone wanting to run 32-bit
non-highmem kernels on this hardware, but disallowing them from
running entirely is surely the safe thing to do.
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave@sr71.net>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luis R. Rodriguez <mcgrof@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Toshi Kani <toshi.kani@hp.com>
Cc: dave.hansen@intel.com
Cc: linux-mm@kvack.org
Cc: mhocko@suse.com
Link: http://lkml.kernel.org/r/20160708001914.D0B50110@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'crypto/cmac.c')
0 files changed, 0 insertions, 0 deletions