[Qemu-ppc] [PATCH for-4.0 0/3] target/ppc: Fix pseries.cap-ibs=workaround with TCG

[Greg Kurz]

Since recent commit 2782ad4c4102 "target/ppc/spapr: Enable mitigations by
default for pseries-4.0 machine type", some recent distros, eg. fedora29,
fail to boot under TCG because of a kernel panic:

[    0.614425] Oops: Exception in kernel mode, sig: 4 [#1]
[    0.618832] LE SMP NR_CPUS=1024 NUMA pSeries
[    0.621868] Modules linked in:
[    0.624958] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 
4.20.16-200.fc29.ppc64le #1
[    0.625978] NIP:  c00000000000bf00 LR: c00000000000e268 CTR: 0000000000007fff
[    0.626572] REGS: c0000000015a3750 TRAP: 0700   Not tainted  
(4.20.16-200.fc29.ppc64le)
[    0.626835] MSR:  8000000002089033 <SF,VEC,EE,ME,IR,DR,RI,LE>  CR: 44828222  
XER: 00000000
[    0.628497] CFAR: c00000000000bee4 IRQMASK: 1 
[    0.628497] GPR00: c00000000001fbc8 c0000000015a39e0 c0000000015a6200 
c000000001533450 
[    0.628497] GPR04: c00000003e5819d0 c00000003ff15f68 0000000000000000 
0000000022f63728 
[    0.628497] GPR08: 0000000000000000 0000000000007fff 0000000000000000 
0000000000000000 
[    0.628497] GPR12: 0000000000008000 c0000000018b0000 000000003dc5fd20 
0000000002e75e90 
[    0.628497] GPR16: 0000000002e75d40 c00000003e594d00 000000003dc5fd20 
0000000002e90b50 
[    0.628497] GPR20: 000000003e45e800 c000000001531a80 c000000001532100 
0000000044828222 
[    0.628497] GPR24: c000000001533450 c000000001533450 c00000003e5819d0 
c0000000010e51e0 
[    0.628497] GPR28: c0000000015d5c18 c000000001531a80 c00000003e580000 
c000000001531a80 
[    0.631710] NIP [c00000000000bf00] flush_count_cache+0x120/0x2420
[    0.631905] LR [c00000000000e268] _switch+0x68/0x180
[    0.632585] Call Trace:
[    0.633490] [c0000000015a39e0] [c0000000015dbd58] __cpu_online_mask+0x0/0x80 
(unreliable)
[    0.634383] [c0000000015a3bc0] [c00000000001fbc8] __switch_to+0x348/0x500
[    0.634614] [c0000000015a3c20] [c000000000c509dc] __schedule+0x2bc/0xac0
[    0.634731] [c0000000015a3cf0] [c000000000c51648] 
preempt_schedule_common+0x38/0x60
[    0.634852] [c0000000015a3d10] [c000000000c516d4] _cond_resched+0x64/0x80
[    0.635527] [c0000000015a3d40] [c00000000011a190] 
copy_process.isra.4.part.5+0xc90/0x1d20
[    0.635656] [c0000000015a3e40] [c00000000011b414] _do_fork+0xd4/0x470
[    0.635772] [c0000000015a3eb0] [c00000000011b88c] kernel_thread+0x3c/0x50
[    0.635891] [c0000000015a3ed0] [c000000000010b08] rest_init+0x98/0xf8
[    0.636025] [c0000000015a3f00] [c000000000fe4084] start_kernel+0x658/0x67c
[    0.636163] [c0000000015a3f90] [c00000000000b37c] 
start_here_common+0x1c/0x520
[    0.636763] Instruction dump:
[    0.640925] 48000005 48000005 48000005 48000005 48000005 4800001c 60000000 
60000000 
[    0.641448] 60000000 60000000 60000000 60000000 <7d2803a6> 39207fff 7d2903a6 
4c400420 
[    0.648580] ---[ end trace 1dcd9494acdef8df ]---
[    0.649361] 
[    1.657870] Kernel panic - not syncing: Attempted to kill the idle task!

The following error is also printed by QEMU:

Opcode 13 10 10 00 (4c400420) leaked temporaries

The root cause behind the panic is that the linux kernel uses for spectre v2
mitigation a form of the bcctr instruction that we don't support. This gets
triggered when passing cap-ibs=workaround machine option, which is the default
since 2782ad4c4102.

The TCG temp leak comes from some missing tcg_temp_free()s on the
exception path.

This series fixes the leak and adds support for the invalid form of bcctr.
Since this adds yet another user of PPC_SEGMENT_64B to discriminate CPU
models that should expose the _new_ behaviour, the final patch introduces
a helper for that purpose.

--
Greg

---

Greg Kurz (3):
      target/ppc: Fix TCG temporary leaks in gen_bcond()
      target/ppc: Enable "decrement and test CTR" version of bcctr
      target/ppc: Consolidate 64-bit server processor detection in a helper


 hw/ppc/ppc.c             |    2 +-
 target/ppc/cpu.h         |    6 +++++
 target/ppc/helper_regs.h |    2 +-
 target/ppc/translate.c   |   58 ++++++++++++++++++++++++++++++++--------------
 4 files changed, 48 insertions(+), 20 deletions(-)