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Re: [PATCH qemu v20] spapr: Implement Open Firmware client interface

From: Alexey Kardashevskiy
Subject: Re: [PATCH qemu v20] spapr: Implement Open Firmware client interface
Date: Sat, 22 May 2021 16:39:57 +1000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:89.0) Gecko/20100101 Thunderbird/89.0 


On 22/05/2021 05:57, BALATON Zoltan wrote:

On Fri, 21 May 2021, BALATON Zoltan wrote:

On Fri, 21 May 2021, Alexey Kardashevskiy wrote:

On 21/05/2021 07:59, BALATON Zoltan wrote:

On Thu, 20 May 2021, Alexey Kardashevskiy wrote:

The PAPR platform 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..e60 - the initial firmware
8000..10000 - stack
400000.. - kernel
3ea0000.. - initramdisk

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 The immediate benefit is much faster booting time which especially 
crucial with fully emulated early CPU bring up environments. Also this
may come handy when/if GRUB-in-the-userspace sees light of the day.

This separates VOF and sPAPR in a hope that VOF bits may be reused by
other POWERPC boards which do not support pSeries.
This is coded in assumption that later on we might be adding support for 
booting from QEMU backends (blockdev is the first candidate) without
devices/drivers in between as OF1275 does not require that and
it is quite easy to so.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---

The example command line is:

/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 8G \
-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 pb/rootfs.cpio.xz \
-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:
v20:
* compile vof.bin with -mcpu=power4 for better compatibility
* s/std/stw/ in entry.S to make it work on ppc32
* fixed dt_available property to support both 32 and 64bit
* shuffled prom_args handling code
* do not enforce 32bit in MSR (again, to support 32bit platforms)



[...]
diff --git a/default-configs/devices/ppc64-softmmu.mak b/default-configs/devices/ppc64-softmmu.mak 
index ae0841fa3a18..9fb201dfacfa 100644
--- a/default-configs/devices/ppc64-softmmu.mak
+++ b/default-configs/devices/ppc64-softmmu.mak
@@ -9,3 +9,4 @@ CONFIG_POWERNV=y
 # For pSeries
 CONFIG_PSERIES=y
 CONFIG_NVDIMM=y
+CONFIG_VOF=y
diff --git a/hw/ppc/Kconfig b/hw/ppc/Kconfig
index e51e0e5e5ac6..964510dfc73d 100644
--- a/hw/ppc/Kconfig
+++ b/hw/ppc/Kconfig
@@ -143,3 +143,6 @@ config FW_CFG_PPC

 config FDT_PPC
     bool
+
+config VOF
+    bool
I think you should just add "select VOF" to config PSERIES section in Kconfig instead of adding it to default-configs/devices/ppc64-softmmu.mak. 

oh well, can do that too.
I think most config options should be selected by KConfig and the default config should only include machines, otherwise VOF would be added also when you don't compile PSERIES or PEGASOS2. With select in Kconfig it will be added when needed. That's why it's better to use select in this case. 


 That should do it, it works in my updated pegasos2 patch:
https://osdn.net/projects/qmiga/scm/git/qemu/commits/3c1fad08469b4d3c04def22044e52b2d27774a61 [...] 
diff --git a/pc-bios/vof/entry.S b/pc-bios/vof/entry.S
new file mode 100644
index 000000000000..569688714c91
--- /dev/null
+++ b/pc-bios/vof/entry.S
@@ -0,0 +1,51 @@
+#define LOAD32(rn, name)    \
+    lis     rn,name##@h;    \
+    ori     rn,rn,name##@l
+
+#define ENTRY(func_name)    \
+    .text;                  \
+    .align  2;              \
+    .globl  .func_name;     \
+    .func_name:             \
+    .globl  func_name;      \
+    func_name:
+
+#define KVMPPC_HCALL_BASE       0xf000
+#define KVMPPC_H_RTAS           (KVMPPC_HCALL_BASE + 0x0)
+#define KVMPPC_H_VOF_CLIENT     (KVMPPC_HCALL_BASE + 0x5)
+
+    . = 0x100 /* Do exactly as SLOF does */
+
+ENTRY(_start)
+#    LOAD32(%r31, 0) /* Go 32bit mode */
+#    mtmsrd %r31,0
+    LOAD32(2, __toc_start)
+    b entry_c
+
+ENTRY(_prom_entry)
+    LOAD32(2, __toc_start)
+    stwu    %r1,-112(%r1)
+    stw     %r31,104(%r1)
+    mflr    %r31
+    bl prom_entry
+    nop
+    mtlr    %r31
+    ld      %r31,104(%r1)
It's getting there, now I see the first client call from the guest boot code but then it crashes on this ld opcode which apparently is 64 bit only: 

Oh right.
Hopefully this is the last such opcode left before I can really test this. 

Make it lwz, and test it?
Yes, figured that out too after sending this message. Replacing with lwz works but I wonder that now you have stwu lwz do the stack offsets need adjusting too or you just waste 4 bytes now? With lwz here I found no further 64 bit opcodes and the guest boot code could walk the device tree. It failed later but I think that's because I'll need to fill more info about the machine in the device tree. I'll experiment with that but it looks like it could work at least for MorphOS. I'll have to try Linux too.
I was trying to get a linux kernel from a debian powerpc iso to do something (debian before 10.0 has Pegasos support) but I've run into the problem that the kernel is loaded at 0x400000 but the start address is at some offset from that. How do I set qemu,boot-kernel in this case?
The pseries kernel can work from any location (and it relocates itself to 0 at some point) even though it is linked at c000.0000.0000.0000, and there is no start address offset: 

===
> objdump -D ~/pbuild/kernel-le/vmlinux
/home/aik/pbuild/kernel-le/vmlinux:     file format elf64-powerpcle


Disassembly of section .head.text:

c000000000000000 <__start>:
c000000000000000:       48 00 00 08     tdi     0,r0,72
c000000000000004: 2c 00 00 48 b c000000000000030 <__start+0x30> 
...
===

Not sure about pegasos2 kernels (or any ppc32 really), sorry.
Because when I set it to the address/size where the kernel is loaded it jumps to the beginnig not the correct start address. If I set the address to the start address then size will be wrong so I don't know how to set qemu,boot-kernel in this case or is there another property to tell the start address? (Vof does not seem to check any other property and seems to assume the entry point is the same as the load address but for this linux kernel it's not.)
I guess if you really need an offset, you'll have to add a new property ("qemu,boot-kernel-start"?) and look for it in the firmware. Or, say, put in gpr5 in your version of spapr_cpu_set_entry_state() and make boot_from_memory() use it. 


--
Alexey
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