On Tue, Jan 18, 2022 at 05:09:25PM +0100, Sven Schnelle wrote: > Hi Mark, Hi Sven, > Mark Rutland <mark.rutland@xxxxxxx> writes: > > On Tue, Jan 18, 2022 at 01:42:26PM +0100, Christian Borntraeger wrote: > >> Will you provide an s390 patch in your next iteration or shall we then do > >> one as soon as there is a v2? We also need to look into vsie.c where we > >> also call sie64a > > > > I'm having a go at that now; my plan is to try to have an s390 patch as > > part of v2 in the next day or so. > > > > Now that I have a rough idea of how SIE and exception handling works on > > s390, I think the structural changes to kvm-s390.c:__vcpu_run() and > > vsie.c:do_vsie_run() are fairly simple. > > > > The only open bit is exactly how/where to identify when the interrupt > > entry code needs to wake RCU. I can add a per-cpu variable or thread > > flag to indicate that we're inside that EQS, or or I could move the irq > > enable/disable into the sie64a asm and identify that as with the OUTSIDE > > macro in the entry asm. > > I wonder whether the code in irqentry_enter() should call a function > is_eqs() instead of is_idle_task(). The default implementation would > be just a > > #ifndef is_eqs > #define is_eqs is_idle_task > #endif > > and if an architecture has special requirements, it could just define > is_eqs() and do the required checks there. This way the architecture > could define whether it's a percpu bit, a cpu flag or something else. I had come to almost the same approach: I've added an arch_in_rcu_eqs() which is checked in addition to the existing is_idle_thread() check. In the case of checking is_idle_thread() and checking for PF_VCPU, I'm assuming the compiler can merge the loads of current->flags, and there's little gain by making this entirely architecture specific, but we can always check that and/or reconsider in future. Thanks, Mark.
