[Qemu-ppc] [PATCH] spapr: don't call KVM_PPC_CONFIGURE_V3_MMU if HPT is in userspace

[Greg Kurz]

Since the kernel commit "dbfcf3cb9c68 powerpc/64: Call H_REGISTER_PROC_TBL
when running as a HPT guest on POWER9", a nested guest running with PR KVM
hangs at boot:

Preparing to boot Linux version 4.16.0-kvm-pr-hang-gku+ (address@hidden) (gcc 
version 8.1.1 20180502 (Red Hat 8.1.1-1) (GCC)) #19 SMP Fri May 25 08:41:55 
CEST 2018
Detected machine type: 0000000000000101
command line: root=UUID=22128c5c-30b1-4e0a-ac16-95853df31131 ro rhgb 
console=hvc0 early_printk disable-radix=on
Max number of cores passed to firmware: 1024 (NR_CPUS = 1024)
Calling ibm,client-architecture-support... done
memory layout at init:
  memory_limit : 0000000000000000 (16 MB aligned)
  alloc_bottom : 0000000001b80000
  alloc_top    : 0000000030000000
  alloc_top_hi : 0000000100000000
  rmo_top      : 0000000030000000
  ram_top      : 0000000100000000
instantiating rtas at 0x000000002fff0000... done
prom_hold_cpus: skipped
copying OF device tree...
Building dt strings...
Building dt structure...
Device tree strings 0x0000000003d90000 -> 0x0000000003d90abb
Device tree struct  0x0000000003da0000 -> 0x0000000003db0000
Quiescing Open Firmware ...
Booting Linux via __start() @ 0x0000000000400000 ...

This happens because the H_REGISTER_PROC_TBL implementation in QEMU
always call KVM_PPC_CONFIGURE_V3_MMU when KVM is present. This fails
in the case of PR KVM, which doesn't implement it, and QEMU returns
H_PARAMETER to the guest, which is a BUG() condition in linux.

In the case of PR, the HPT is allocated in userspace by QEMU, so it
doesn't make sense to call KVM_PPC_CONFIGURE_V3_MMU in the first
place. So, skip it in this case and let the guest boot.

Signed-off-by: Greg Kurz <address@hidden>
---

Note that PR KVM requires this patch from Paul to work on POWER9:

    https://patchwork.ozlabs.org/patch/916766/

The original request was coming from people who want to run openQA in
fedora28 under PowerVM on a POWER9 system. This requires PR KVM, which
will be running in HPT-mode since pHyp doesn't do radix.

Cc'ing stable because fedora28 ships QEMU 2.11.x.
---
 hw/ppc/spapr_hcall.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
index 022f6d810182..12cbb317e5e8 100644
--- a/hw/ppc/spapr_hcall.c
+++ b/hw/ppc/spapr_hcall.c
@@ -1420,7 +1420,7 @@ static target_ulong h_register_process_table(PowerPCCPU 
*cpu,
                   ((flags & FLAG_GTSE) ? LPCR_GTSE : 0),
                   LPCR_UPRT | LPCR_GTSE);
 
-    if (kvm_enabled()) {
+    if (kvm_enabled() && !spapr->htab) {
         return kvmppc_configure_v3_mmu(cpu, flags & FLAG_RADIX,
                                        flags & FLAG_GTSE, cproc);
     }