Excerpts from Fabiano Rosas's message of March 24, 2021 4:03 am: > Nicholas Piggin <npiggin@xxxxxxxxx> writes: > >> In the interest of minimising the amount of code that is run in >> "real-mode", don't handle hcalls in real mode in the P9 path. >> >> POWER8 and earlier are much more expensive to exit from HV real mode >> and switch to host mode, because on those processors HV interrupts get >> to the hypervisor with the MMU off, and the other threads in the core >> need to be pulled out of the guest, and SLBs all need to be saved, >> ERATs invalidated, and host SLB reloaded before the MMU is re-enabled >> in host mode. Hash guests also require a lot of hcalls to run. The >> XICS interrupt controller requires hcalls to run. >> >> By contrast, POWER9 has independent thread switching, and in radix mode >> the hypervisor is already in a host virtual memory mode when the HV >> interrupt is taken. Radix + xive guests don't need hcalls to handle >> interrupts or manage translations. >> >> So it's much less important to handle hcalls in real mode in P9. >> >> Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx> > > I tried this again in the L2 with xive=off and it works as expected now. > > Tested-by: Fabiano Rosas <farosas@xxxxxxxxxxxxx> Oh good, thanks for spotting the problem and re testing. Thanks, Nick
