Hi Jintack, On Tue, Jul 18, 2017 at 10:23:05PM -0400, Jintack Lim wrote: > On Tue, Jul 18, 2017 at 12:58 PM, Jintack Lim <jintack.lim@xxxxxxxxxx> wrote: > > Nested virtualization is the ability to run a virtual machine inside another > > virtual machine. In other words, it’s about running a hypervisor (the guest > > hypervisor) on top of another hypervisor (the host hypervisor). > > > > Supporting nested virtualization on ARM means that the hypervisor provides not > > only EL0/EL1 execution environment to VMs as it usually does but also the > > virtualization extensions including EL2 execution environment. Once the host > > hypervisor provides those execution environments to the VMs, then the guest > > hypervisor can run its own VMs (nested VMs) naturally. > > > > This series supports nested virtualization on arm64. ARM recently announced an > > extension (ARMv8.3) which has support for nested virtualization[1]. This patch > > set is based on the ARMv8.3 specification and tested on the FastModel with > > ARMv8.3 extension. > > > > The whole patch set to support nested virtualization is huge over 70 > > patches, so I categorized them into four parts: CPU, memory, VGIC, and timer > > virtualization. This patch series is the first part. > > > > CPU virtualization patch series provides basic nested virtualization framework > > and instruction emulations including v8.1 VHE feature and v8.3 nested > > virtualization feature for VMs. > > > > This patch series again can be divided into four parts. Patch 1 to 5 introduces > > nested virtualization by discovering hardware feature, adding a kernel > > parameter and allowing the userspace to set the initial CPU mode to EL2. > > > > Patch 6 to 25 are to support the EL2 execution environment, the virtual EL2, to > > a VM on v8.0 architecture. We de-privilege the guest hypervisor and emulate the > > virtual EL2 mode in EL1 using the hardware features provided by ARMv8.3; The > > host hypervisor manages virtual EL2 register state for the guest hypervisor > > and shadow EL1 register state that reflects the virtual EL2 register state to > > run the guest hypervisor in EL1. > > > > Patch 26 to 33 add support for the virtual EL2 with Virtualization Host > > Extensions. These patches emulate newly defined registers and bits in v8.1 and > > allow the virtual EL2 to access EL2 register states via EL1 register accesses > > as in the real EL2. > > > > Patch 34 to 38 are to support for the virtual EL2 with nested virtualization. > > These enable recursive nested virtualization. > > > > This patch set is tested on the FastModel with the v8.3 extension for arm64 and > > a cubietruck for arm32. On the FastModel, the host and the guest kernels are > > compiled with and without VHE, so there are four combinations. I was able to > > boot SMP Linux in the nested VM on all four configurations and able to run > > hackbench. I also checked that regular VMs could boot when the nested > > virtualization kernel parameter was not set. On the cubietruck, I also verified > > that regular VMs could boot as well. > > > > I'll share my experiment setup shortly. > > I summarized my experiment setup here. > > https://github.com/columbia/nesting-pub/wiki/Nested-virtualization-on-ARM-setup > Thanks for sharing this. > > > > Even though this work has some limitations and TODOs, I'd appreciate early > > feedback on this RFC. Specifically, I'm interested in: > > > > - Overall design to manage vcpu context for the virtual EL2 > > - Verifying correct EL2 register configurations such as HCR_EL2, CPTR_EL2 > > (Patch 30 and 32) > > - Patch organization and coding style > > I also wonder if the hardware and/or KVM do not support nested > virtualization but the userspace uses nested virtualization option, > which one is better: giving an error or launching a regular VM > silently. > I think KVM should complain to userspace if userspace tries to set a feature it does not support, and I think userspace should give as meaningful an error message as possible to the user when that happens. Thanks, -Christoffer
