Re: [RFC PATCH v2 07/19] RISC-V: KVM: Implement KVM_GET_ONE_REG/KVM_SET_ONE_REG ioctls

[Paolo Bonzini]

On 05/08/19 13:37, Christian Borntraeger wrote:
> While have ONE_REG will certainly work, have you considered the sync_reg scheme
> (registers as part of kvm_run structure)
> This will speed up the exit to QEMU as you do not have to do multiple ioctls
> (each imposing a systemcall overhead) for one exit. 
> 
> Ideally you should not exit too often into qemu, but for those cases sync_regs
> is faster than ONE_REG.

At least in theory, RISC-V should never have exits to QEMU that need
accessing the registers.  (The same is true for x86; Google implemented
sync_regs because they moved the instruction emulator to userspace in
their fork).

Paolo