Hi, Dave, On Thu, Jul 23, 2020 at 09:23:13AM -0700, Dave Hansen wrote: > On 7/23/20 9:18 AM, Fenghua Yu wrote: > > The PKRS MSR has been preserved in thread_info during kernel entry. We > > don't need to preserve it in another place (i.e. idtentry_state). > > I'm missing how the PKRS MSR gets preserved in thread_info. Could you > explain the mechanism by which this happens and point to the code > implementing it, please? [Sorry, my mistake: I mean "thread_struct" instead of "thread_info". Hopefully the typo doesn't change the essential part in my last email.] The "saved_pkrs" is defined in thread_struct and context switched in patch 04/17: https://lore.kernel.org/lkml/20200717072056.73134-5-ira.weiny@xxxxxxxxx/ Because there is no XSAVE support the PKRS MSR, we preserve it in "saved_pkrs" in thread_struct. It's initialized as 0 (init state, no protection key) in fork() or exec(). It's updated to a right protection value when a driver calls the updating API. The PKRS MSR is context switched by "saved_pkrs" when switching to a task (unless optimized if the cached MSR is the same as the saved one). Thanks. -Fenghua
