Support PVH boot protocol

[bonzini]

The PVH boot protocol allows loading an uncompressed kernel instead of a bzImage. This is faster as it removes decompression from the total startup time.

[sameo]

@bonzini For direct kernel boot (no fw), what does PVH bring compared to our current vmlinux loader?
Can it be seen as a more generic way of loading any ELF kernel image (e.g. FreeBSD)?

[aljimenezb]

I am working on a PoC implementing PVH boot support on Firecracker. Currently debugging an early boot issue, will send a request for code comments once I have a working prototype.

[bonzini]

PVH has a much smaller set of boot parameters than the Linux boot protocol (just the e820 memory map, basically), so it's simpler to launch than a generic vmlinux.

Other OSes may indeed support PVH more easily than the Linux boot protocol, but typically they only enable PVH for Xen support and do Xen-specific stuff in the PVH boot code. However, in principle it would be possible to add support for PVH-on-KVM to them, as well.

[sameo]

PVH has a much smaller set of boot parameters than the Linux boot protocol (just the e820 memory map, basically), so it's simpler to launch than a generic vmlinux.

Ok, I see, thanks.

[sameo]

I am working on a PoC implementing PVH boot support on Firecracker. Currently debugging an early boot issue, will send a request for code comments once I have a working prototype.

@aljimenezb Cool. Are you planning to contribute this code to the rust-vmm crate as well?

[aljimenezb]

I am working on a PoC implementing PVH boot support on Firecracker. Currently debugging an early boot issue, will send a request for code comments once I have a working prototype.

@aljimenezb Cool. Are you planning to contribute this code to the rust-vmm crate as well?

@sameo Yes, that is the goal.

[rbradford]

@aljimenezb Any update on your PVH work?

[aljimenezb]

@aljimenezb Any update on your PVH work?

Hi @rbradford. I have prototype code that extracts the PVH entry point from the ELF note in the kernel binary. I have also made changes to configure the initial register state and memory map, but the guest dies right after jumping to the entry point, so I am currently working on debugging that. I was planning to ask for advice on the firecracker and/or rust-vmm Slack, maybe I can ping you there?