On 8 November 2012 15:29, Jessica Allison <jessica.allison.2012@xxxxxxxxxxx> wrote: > Hi there, I am developing a boot loader for Linux KVM on ARM. Can you just > confirm to me that for KVM to work it is required that the kernel is > booted in HYP mode? Yes. The ABI contract between the boot loader and the kernel mandates that you pass the kernel control in Hyp mode if you want KVM to work. This is all now documented in https://github.com/torvalds/linux/blob/master/Documentation/arm/Booting > Is there no way for KVM to later switch to HYP mode when the kernel > is booted in non-secure SVC mode? If you are in NS-SVC then the only way to get back up to Hyp mode would be (a) to make a hypercall via the HVC insn or (b) to make a secure monitor call via the SMC insn. This would require that we made the boot loader provide some ABI for "give me hypervisor access". This is much more complicated and easy for boot loader authors to get wrong or fail to implement. So we do the simple straightforward thing and just require the boot loader to pass us control in the most privileged mode possible. We don't let bootloaders start the kernel in user mode and provide an ABI for giving us access to SVC mode later either :-) -- PMM _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/cucslists/listinfo/kvmarm
