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

[Suraj Jitindar Singh]

On Fri, 2019-03-22 at 19:03 +0100, Greg Kurz wrote:
> 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:

Good catch! I noticed this as well but didn't get around to fixing it
so thanks for doing it for me :D

> 
> [    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(-)
> 
>