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? - 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). 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
