On 19.01.2018 11:11, Heiko Carstens wrote: > On Thu, Jan 18, 2018 at 09:45:03PM +0100, David Hildenbrand wrote: >> Actually, the problem is there are no atomic byte-based operations on >> s390x without Interlocked-Access-Facility 2. >> >> Even __sync_fetch_and_or(&gisa->ipm, value) falls back to a >> Compare-And-Swap loop. And Compare-And-Swap also operates at least on 32bit. >> >> So I assume there isn't too much we can do about it. As storage >> locations following the u8 are also written - but in an atomic matter, >> it should in general not matter. >> >> But can we avoid starting the bitmap at the beginning of the gisa? >> >> What about something like this: >> >> +void kvm_s390_gisa_set_ipm_gisc(struct kvm_s390_gisa *gisa, u8 gisc) >> +{ >> + set_bit_inv(gisc, (unsigned long *) &gisa->ipm); >> +} > > set_bit_inv() may use a csg instruction which requires an 8 byte alignment > of the operand. What you propose would crash immediately. > > The code written by Michael is fine as-is. > That's unfortunate... and still looks hacky to me :) But if it works ... -- Thanks, David / dhildenb -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html