On Wed, Jul 19, 2017 at 4:49 AM, Christoffer Dall <cdall@xxxxxxxxxx> wrote: > 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. > Ok, thanks. I'll work this out. > Thanks, > -Christoffer
