Nicholas Piggin <npig...@gmail.com> writes: > Michael Ellerman's on January 17, 2019 9:35 pm: >> 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> > > But only because spectre and meltdown broke my spirit.
ðŸ˜ðŸ˜ðŸ˜ðŸ˜ðŸ˜ðŸ˜ðŸ˜ðŸ˜ðŸ˜ðŸ˜ Thanks for reviewing it anyway. cheers
