On Thu, 2019-01-17 at 11:35:10 UTC, Michael Ellerman wrote: > Currently in system_call_exit() we have an optimisation where we > disable MSR_RI (recoverable interrupt) and MSR_EE (external interrupt > enable) in a single mtmsrd instruction. > > Unfortunately this will no longer work with THREAD_INFO_IN_TASK, > because then the load of TI_FLAGS might fault and faulting with MSR_RI > clear is treated as an unrecoverable exception which leads to a > panic(). > > So change the code to only clear MSR_EE prior to loading TI_FLAGS, > leaving the clear of MSR_RI until later. We have some latitude in > where do the clear of MSR_RI. A bit of experimentation has shown that > this location gives the least slow down. > > This still causes a noticeable slow down in our null_syscall > performance. On a Power9 DD2.2: > > Before After Delta Delta % > 955 cycles 999 cycles -44 -4.6% > > On the plus side this does simplify the code somewhat, because we > don't have to reenable MSR_RI on the restore_math() or > syscall_exit_work() paths which was necessitated previously by the > optimisation. > > Signed-off-by: Michael Ellerman <m...@ellerman.id.au> > Reviewed-by: Nicholas Piggin <npig...@gmail.com>
Applied to powerpc next. https://git.kernel.org/powerpc/c/e7fda7e569e1776d4dccbcef52d34882 cheers
