Re: [PATCH qemu v12] spapr: Implement Open Firmware client interface

[Greg Kurz]

On Fri, 18 Dec 2020 13:50:40 +1100
Alexey Kardashevskiy <aik@ozlabs.ru> wrote:

> The PAPR platform which describes an OS environment that's presented by
> a combination of a hypervisor and firmware. The features it specifies
> require collaboration between the firmware and the hypervisor.
> 
> Since the beginning, the runtime component of the firmware (RTAS) has
> been implemented as a 20 byte shim which simply forwards it to
> a hypercall implemented in qemu. The boot time firmware component is
> SLOF - but a build that's specific to qemu, and has always needed to be
> updated in sync with it. Even though we've managed to limit the amount
> of runtime communication we need between qemu and SLOF, there's some,
> and it has become increasingly awkward to handle as we've implemented
> new features.
> 
> This implements a boot time OF client interface (CI) which is
> enabled by a new "x-vof" pseries machine option (stands for "Virtual Open
> Firmware). When enabled, QEMU implements the custom H_OF_CLIENT hcall
> which implements Open Firmware Client Interface (OF CI). This allows
> using a smaller stateless firmware which does not have to manage
> the device tree.
> 
> The new "vof.bin" firmware image is included with source code under
> pc-bios/. It also includes RTAS blob.
> 
> This implements a handful of CI methods just to get -kernel/-initrd
> working. In particular, this implements the device tree fetching and
> simple memory allocator - "claim" (an OF CI memory allocator) and updates
> "/memory@0/available" to report the client about available memory.
> 
> This implements changing some device tree properties which we know how
> to deal with, the rest is ignored. To allow changes, this skips
> fdt_pack() when x-vof=on as not packing the blob leaves some room for
> appending.
> 
> In absence of SLOF, this assigns phandles to device tree nodes to make
> device tree traversing work.
> 
> When x-vof=on, this adds "/chosen" every time QEMU (re)builds a tree.
> 
> This adds basic instances support which are managed by a hash map
> ihandle -> [phandle].
> 
> Before the guest started, the used memory is:
> 0..4000 - the initial firmware
> 10000..180000 - stack
> 
> This OF CI does not implement "interpret".
> 
> Unlike SLOF, this does not format uninitialized nvram. Instead, this
> includes a disk image with pre-formatted nvram.
> 
> With this basic support, this can only boot into kernel directly.
> However this is just enough for the petitboot kernel and initradmdisk to
> boot from any possible source. Note this requires reasonably recent guest
> kernel with:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=df5be5be8735
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
> 
> The example command line is:
> 
> -c 0 /home/aik/pbuild/qemu-killslof-localhost-ppc64/qemu-system-ppc64 \
> -nodefaults \
> -chardev stdio,id=STDIO0,signal=off,mux=on \
> -device spapr-vty,id=svty0,reg=0x71000110,chardev=STDIO0 \
> -mon id=MON0,chardev=STDIO0,mode=readline \
> -nographic \
> -vga none \
> -enable-kvm \
> -m 2G \
> -machine 
> pseries,x-vof=on,cap-cfpc=broken,cap-sbbc=broken,cap-ibs=broken,cap-ccf-assist=off
>  \
> -kernel pbuild/kernel-le-guest/vmlinux \
> -initrd t/le.cpio \
> -drive 
> id=DRIVE0,if=none,file=./p/qemu-killslof/pc-bios/vof/nvram.bin,format=raw \
> -global spapr-nvram.drive=DRIVE0 \
> -snapshot \
> -smp 8,threads=8 \
> -L /home/aik/t/qemu-ppc64-bios/ \
> -trace events=qemu_trace_events \
> -d guest_errors \
> -chardev socket,id=SOCKET0,server,nowait,path=qemu.mon.tmux26 \
> -mon chardev=SOCKET0,mode=control
> 
> ---
> Changes:
> v12:
> * split VOF and SPAPR
> 

Thanks for the split. The VOF paths are now clearly identified in
the sPAPR code, and well guarded by a check on x-vof. Rest of the
patch looks good to me. I gave it a try with a stock fedora 33
kernel and initramfs and it booted really fast !

With the checkpatch complaints addressed,

Acked-by: Greg Kurz <groug@kaod.org>

and

Tested-by: Greg Kurz <groug@kaod.org>