On Wed, Oct 03, 2018 at 04:13:36PM +1000, David Gibson wrote: > On Tue, Oct 02, 2018 at 09:31:28PM +1000, Paul Mackerras wrote: > > From: Suraj Jitindar Singh <sjitindarsingh@xxxxxxxxx> > > > > The hcall H_ENTER_NESTED takes as the two parameters the address in > > L1 guest memory of a hv_regs struct and a pt_regs struct which the > > L1 guest would like to use to run a L2 guest and in which are returned > > the exit state of the L2 guest. For efficiency, these are in the > > endianness of the L1 guest, rather than being always big-endian as is > > usually the case for PAPR hypercalls. > > Does that actually make a difference for efficiency? I thought the > presence of the byte-reversing loads and stores meant byteswapping was > basically zero-cost on POWER. It means that the L1 hypervisor can pass a pointer to the regs struct in the kvm_vcpu struct rather than having to make a copy, and copy the values back after the H_ENTER_NESTED. I'll reword the commit message to say it's mostly about convenience and to a lesser extent about performance. Paul.
