diff options
| author | Cyril Bur <cyrilbur@gmail.com> | 2016-09-23 16:18:08 +1000 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2016-10-04 16:43:05 +1100 |
| commit | dc16b553c949e81f37555777dc7bab66d78285a7 (patch) | |
| tree | 232193ebddf36323a7611d5118e5bdad540edde5 | |
| parent | 0e7736c6b806b24c693367196a076c78328ed742 (diff) | |
powerpc: Always restore FPU/VEC/VSX if hardware transactional memory in use
Comment from arch/powerpc/kernel/process.c:967:
If userspace is inside a transaction (whether active or
suspended) and FP/VMX/VSX instructions have ever been enabled
inside that transaction, then we have to keep them enabled
and keep the FP/VMX/VSX state loaded while ever the transaction
continues. The reason is that if we didn't, and subsequently
got a FP/VMX/VSX unavailable interrupt inside a transaction,
we don't know whether it's the same transaction, and thus we
don't know which of the checkpointed state and the ransactional
state to use.
restore_math() restore_fp() and restore_altivec() currently may not
restore the registers. It doesn't appear that this is more serious
than a performance penalty. If the math registers aren't restored the
userspace thread will still be run with the facility disabled.
Userspace will not be able to read invalid values. On the first access
it will take an facility unavailable exception and the kernel will
detected an active transaction, at which point it will abort the
transaction. There is the possibility for a pathological case
preventing any progress by transactions, however, transactions
are never guaranteed to make progress.
Fixes: 70fe3d9 ("powerpc: Restore FPU/VEC/VSX if previously used")
Signed-off-by: Cyril Bur <cyrilbur@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>