Re: [Qemu-devel] sparc: crash when using initrd > 5M

[Corentin Labbe]

On Fri, Feb 01, 2019 at 02:15:15PM +0000, Mark Cave-Ayland wrote:
> On 18/01/2019 13:33, Mark Cave-Ayland wrote:
> 
> > On 03/01/2019 15:48, Corentin Labbe wrote:
> > 
> >> Hello
> >>
> >> When using an initrd > 5M, I hit the following kernel crash:
> >> qemu-system-sparc -kernel vmlinux -initrd rootfs.cpio.gz -nographic
> >> Configuration device id QEMU version 1 machine id 32
> >> Probing SBus slot 0 offset 0
> >> Probing SBus slot 1 offset 0
> >> Probing SBus slot 2 offset 0
> >> Probing SBus slot 3 offset 0
> >> Probing SBus slot 4 offset 0
> >> Probing SBus slot 5 offset 0
> >> Invalid FCode start byte
> >> CPUs: 1 x FMI,MB86904
> >> UUID: 00000000-0000-0000-0000-000000000000
> >> Welcome to OpenBIOS v1.1 built on Oct 5 2018 08:20
> >>   Type 'help' for detailed information
> >> [sparc] Kernel already loaded
> >> switching to new context:
> >> PROMLIB: obio_ranges 1
> >> [    0.000000] PROMLIB: Sun Boot Prom Version 3 Revision 2
> >> [    0.000000] Linux version 4.20.0-next-20190102+ (address@hidden) (gcc 
> >> version 7.3.0 (Gentoo 7.3.0-r3 p1.4)) #148 Thu Jan 3 16:17:08 CET 2019
> >> [    0.000000] printk: bootconsole [earlyprom0] enabled
> >> [    0.000000] ARCH: SUN4M
> >> [    0.000000] TYPE: SPARCstation 5
> >> [    0.000000] Ethernet address: 52:54:00:12:34:56
> >> [    0.000000] Unable to handle kernel NULL pointer dereference
> >> [    0.000000] tsk->{mm,active_mm}->context = ffffffff
> >> [    0.000000] tsk->{mm,active_mm}->pgd = 00000000
> >> [    0.000000]               \|/ ____ \|/
> >> [    0.000000]               "@'/ ,. \`@"
> >> [    0.000000]               /_| \__/ |_\
> >> [    0.000000]                  \__U_/
> >> [    0.000000] swapper(0): Oops [#1]
> >> [    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 
> >> 4.20.0-next-20190102+ #148
> >> [    0.000000] PSR: 04001fc0 PC: f0010ef0 NPC: f0010ef4 Y: 00000000    Not 
> >> tainted
> >> [    0.000000] PC: <do_sparc_fault+0x158/0x404>
> >> [    0.000000] %G: 0000000a 000003c4  f05ece08 f05ecc00  00000000 00e00000 
> >>  f05d4000 00000001
> >> [    0.000000] %O: 00000000 00e00000  00800000 00e00000  00000000 00000002 
> >>  f05d5bb8 f00bba58
> >> [    0.000000] RPC: <memblock_reserve+0x38/0x68>
> >> [    0.000000] %L: 00000040 f05dfaf8  f05d5c68 00000001  0003ffff 006951e0 
> >>  f05ed014 f0674ab4
> >> [    0.000000] %I: f05d5c80 00000000  00000002 f1000000  ffffffff 00000000 
> >>  f05d5c20 f0007fd8
> >> [    0.000000] Disabling lock debugging due to kernel taint
> >> [    0.000000] Caller[f0007fd8]: srmmu_fault+0x58/0x68
> >> [    0.000000] Caller[f0618598]: memblock_alloc_try_nid+0xb8/0xc8
> >> [    0.000000] Caller[f0611094]: srmmu_paging_init+0x174/0xaf8
> >> [    0.000000] Caller[f06106a8]: paging_init+0x4/0x24
> >> [    0.000000] Caller[f060e4f0]: setup_arch+0x3e8/0x480
> >> [    0.000000] Caller[f060ab50]: start_kernel+0x48/0x460
> >> [    0.000000] Caller[f060a43c]: continue_boot+0x324/0x334
> >> [    0.000000] Caller[00000000]:   (null)
> >> [    0.000000] Instruction DUMP:
> >> [    0.000000]  c800a024 
> >> [    0.000000]  83286002 
> >> [    0.000000]  073c17b3 
> >> [    0.000000] <c4010001>
> >> [    0.000000]  c600e22c 
> >> [    0.000000]  8a08a003 
> >> [    0.000000]  80a16001 
> >> [    0.000000]  0280003b 
> >> [    0.000000]  c600c001 
> >> [    0.000000] 
> >> [    0.000000] Kernel panic - not syncing: Attempted to kill the idle task!
> >> [    0.000000] Press Stop-A (L1-A) from sun keyboard or send break
> >> [    0.000000] twice on console to return to the boot prom
> >> [    0.000000] ---[ end Kernel panic - not syncing: Attempted to kill the 
> >> idle task! ]---
> >> qemu-system-sparc: terminating on signal 15 from pid 13043 (killall)
> >>
> >> The NULL ptr dereference is done by memset() in srmmu_nocache_init() and 
> >> memblock_alloc_try_nid().
> >> If I comment both memset, the boot pass
> >>
> >> But since nothing explain the NULL ptr deref in memset(), I suspect 
> >> something is overriden by the initrd
> > 
> > Sorry about the delay in replying to this, I haven't been too well recently.
> > 
> > Looking at the code I suspect the problem is that when loading a kernel 
> > directly,
> > OpenBIOS isn't adding the kernel/initrd memory ranges to the DT properties, 
> > and so
> > the kernel doesn't recreate its own mapping on boot.
> > 
> > It shouldn't be too hard to make this happen, let me take and look and see 
> > how
> > difficult this would be.
> 
> I think I now have a fix for this, with changes needed in both QEMU and 
> OpenBIOS.
> 
> Firstly you'll need to apply the QEMU patch from
> https://lists.gnu.org/archive/html/qemu-devel/2019-01/msg06635.html and then 
> you'll
> need an updated OpenBIOS.
> 
> I've uploaded a pre-compiled openbios-sparc32 with the patches from
> https://mail.coreboot.org/hyperkitty/list/address@hidden/thread/E6IMJNUFRF7W6ALWSYBOOCEYLBFXXQEN/
> to https://www.ilande.co.uk/tmp/qemu/openbios-sparc32-initrdfix for testing.
> 
> Please can you test and let me know if this solves the issue? If so, I'll see 
> if I
> can get them merged in time for the upcoming QEMU 4.0 release.
> 

Hello

Sorry even with the patch I still hit the issue.

I have added some debug and at least qemu set initrd_size correctly now.

I have tried to compile openbios-sparc32 for debugging but fail with
arch/sparc32/context.c:116:5: error: PIC register clobbered by 'l7' in 'asm'
     asm __volatile__ ("\n\tcall __switch_context"
     ^~~
make[1]: *** [rules.mak:219: target/arch/sparc32/context.o] Error 1
(gcc 7.2 and gc 6.4 with binutils 2.30)

Regards