On Sun, Nov 22, 2020 at 06:56:24AM +0000, Chatradhi, Naveen Krishna wrote: > [AMD Official Use Only - Approved for External Use] > > Hi Guenter, Salvatore > > > This is very unusual, and may mess up the "sensors" command. > > What problem is this trying to solve ? > Guenter, sorry for the delayed response. > This fix is required to address the possible side channel attack reported in CVE-2020-12912. > [ ... ] > > >> ? > Yes, Salvatore, thanks for bringing the links. > A much better fix would have been to cache RAPL data for a short period of time. To avoid any possibility of attacks, maybe add some random interval. Something like this: In accumulate_delta(): accums->next_update = jiffies + HZ / 2 + get_random_int % HZ; In amd_energy_read(): accum = &data->accums[channel]; if (time_after(accum->next_update)) accumulate_delta(data, channel, cpu, reg); *val = div64_ul(accum->energy_ctr * 1000000UL, BIT(data->energy_units)); and drop amd_add_delta(). Guenter
