4.4-stable review patch. If anyone has any objections, please let me know.
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From: Aneesh Kumar K.V aneesh.kumar@linux.ibm.com
commit 91d06971881f71d945910de128658038513d1b24 upstream.
Currently we do not have an isync, or any other context synchronizing instruction prior to the slbie/slbmte in _switch() that updates the SLB entry for the kernel stack.
However that is not correct as outlined in the ISA.
From Power ISA Version 3.0B, Book III, Chapter 11, page 1133:
"Changing the contents of ... the contents of SLB entries ... can have the side effect of altering the context in which data addresses and instruction addresses are interpreted, and in which instructions are executed and data accesses are performed. ... These side effects need not occur in program order, and therefore may require explicit synchronization by software. ... The synchronizing instruction before the context-altering instruction ensures that all instructions up to and including that synchronizing instruction are fetched and executed in the context that existed before the alteration."
And page 1136:
"For data accesses, the context synchronizing instruction before the slbie, slbieg, slbia, slbmte, tlbie, or tlbiel instruction ensures that all preceding instructions that access data storage have completed to a point at which they have reported all exceptions they will cause."
We're not aware of any bugs caused by this, but it should be fixed regardless.
Add the missing isync when updating kernel stack SLB entry.
Cc: stable@vger.kernel.org Signed-off-by: Aneesh Kumar K.V aneesh.kumar@linux.ibm.com [mpe: Flesh out change log with more ISA text & explanation] Signed-off-by: Michael Ellerman mpe@ellerman.id.au Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/powerpc/kernel/entry_64.S | 1 + 1 file changed, 1 insertion(+)
--- a/arch/powerpc/kernel/entry_64.S +++ b/arch/powerpc/kernel/entry_64.S @@ -574,6 +574,7 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_1T_SEG * actually hit this code path. */
+ isync slbie r6 slbie r6 /* Workaround POWER5 < DD2.1 issue */ slbmte r7,r0