On Thu, Jun 21, 2018 at 09:55:40PM +0200, Peter Zijlstra wrote: > On Sun, May 27, 2018 at 08:45:53AM -0700, Fenghua Yu wrote: > > set_bit() called by set_cpu_cap() is a locked bit set instruction for > > atomic operation. > > > > Since the c->x86_capability can span two cache lines depending on kernel > > configuration and building evnironment, the locked bit set instruction may > > cause #AC exception when #AC exception for split lock is enabled. > > That doesn't make sense. Sure the bitmap may be longer, but depending on > if the argument is an immediate or not we either use a byte instruction > (which can never cross a cacheline boundary) or a 'word' aligned BTS. > And the bitmap really _should_ be 'unsigned long' aligned. > > If it is not aligned, fix that too. > > /me looks at cpuinfo_x86 and finds x86_capability is in fact a __u32 > array.. see that's broken and needs fixing first.
Do you mean x86_capability's type should be changed from __u32 to unsigned long? Changing x86_capability's type won't directly fix the split lock in set_cpu_cap(), right? BTS still may access x86_capability across cache line no matter x86_capability's type. Thanks. -Fenghua
