On 17 September 2018 at 11:41, Suzuki K Poulose <suzuki.poulose@xxxxxxx> wrote: > --- a/Documentation/virtual/kvm/api.txt > +++ b/Documentation/virtual/kvm/api.txt > @@ -122,6 +122,14 @@ the default trap & emulate implementation (which changes the virtual > memory layout to fit in user mode), check KVM_CAP_MIPS_VZ and use the > flag KVM_VM_MIPS_VZ. > > +To configure the physical address space size for a VM (IPA size) on arm64, > +check KVM_CAP_ARM_VM_PHYS_SHIFT (which returns the maximum limit for the > +IPA shift) and use KVM_VM_TYPE_ARM_PHYS_SHIFT(PHYS_SHIFT). Bits[7-0] of the > +machine type has been reserved for specifying the PHYS_SHIFT. > +The supported range is [32...IPA_LIMIT], where IPA_LIMIT could be > +identified by checking KVM_CAP_ARM_VM_PHYS_SHIFT. For backward compatibility > +a value of 0 selects 40bits. > + Given this as the API documentation, I don't think I could figure out what I as a userspace user of it need to do without looking at the kernel code. Could I ask you to expand it so that it is a bit less terse and a bit more detailed? (For instance, what is a PHYS_SHIFT and why do I have to specify it rather than just telling the kernel I want a 48 bit guest address space?) thanks -- PMM
