On 2015-08-26 11:28, Antonios Motakis wrote: > > > On 26-Aug-15 11:21, Jan Kiszka wrote: >> On 2015-08-26 11:12, Antonios Motakis wrote: >>> Hello Marc, >>> >>> On 08-Jul-15 18:19, Marc Zyngier wrote: >>>> ARMv8.1 comes with the "Virtualization Host Extension" (VHE for >>>> short), which enables simpler support of Type-2 hypervisors. >>>> >>>> This extension allows the kernel to directly run at EL2, and >>>> significantly reduces the number of system registers shared between >>>> host and guest, reducing the overhead of virtualization. >>>> >>>> In order to have the same kernel binary running on all versions of the >>>> architecture, this series makes heavy use of runtime code patching. >>>> >>>> The first ten patches massage the KVM code to deal with VHE and enable >>>> Linux to run at EL2. >>> >>> I am currently working on getting the Jailhouse hypervisor to work on >>> AArch64. >>> >>> I've been looking at your patches, trying to figure out the implications >>> for Jailhouse. It seems there are a few :) >>> >>> Jailhouse likes to be loaded by Linux into memory, and then to inject >>> itself at a higher level than Linux (demoting Linux into being the "root >>> cell"). This works on x86 and ARM (AArch32 and eventually AArch64 without >>> VHE). What this means in ARM, is that Jailhouse hooks into the HVC stub >>> exposed by Linux, and happily installs itself in EL2. >>> >>> With Linux running in EL2 though, that won't be as straightforward. It >>> looks like we can't just demote Linux to EL1 without breaking something. >>> Obviously it's OK for us that KVM won't work, but it looks like at least >>> the timer code will break horribly if we try to do something like that. >>> >>> Any comments on this? One work around would be to just remap the incoming >>> interrupt from the timer, so Linux never really realizes it's not running >>> in EL2 anymore. Then we would also have to deal with the intricacies of >>> removing and re-adding vCPUs to the Linux root cell, so we would have to >>> maintain the illusion of running in EL2 for each one of them. >> >> Without knowing any of the details, I would say there are two strategies >> regarding this: >> >> - Disable KVM support in the Linux kernel - then we shouldn't boot into >> EL2 in the first place, should we? > > We would have to ask the user to patch the kernel, to ignore VHE and keep all > the hyp stub magic that we rely on currently. It is an option of course.
Patch or reconfigure? CONFIG_KVM isn't mandatory for arm64, is it? Jan > >> >> - Emulate what Linux is missing after take-over by Jailhouse (we do >> this on x86 with VT-d interrupt remapping which cannot be disabled >> anymore for Linux once it started with it, and we cannot boot without >> it when we want to use the x2APIC). > > Essentially what I described above; let's call it nested virtualization > without the virtualization parts? :) > >> >> Jan >> > -- Siemens AG, Corporate Technology, CT RTC ITP SES-DE Corporate Competence Center Embedded Linux -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
