Subject: Re: [PATCH] powerpc/pseries: Fix xive=off command line

From: Michael Ellerman <[email-masked]>
Date: Mon, 3 Jun 2019 22:32:51 +1000 (AEST)

On Wed, 2019-05-15 at 10:05:01 UTC, Greg Kurz wrote:
> On POWER9, if the hypervisor supports XIVE exploitation mode, the guest OS
> will unconditionally requests for the XIVE interrupt mode even if XIVE was
> deactivated with the kernel command line xive=off. Later on, when the spapr
> XIVE init code handles xive=off, it disables XIVE and tries to fall back on
> the legacy mode XICS.
> 
> This discrepency causes a kernel panic because the hypervisor is configured
> to provide the XIVE interrupt mode to the guest :
> 
> [    0.008837] kernel BUG at arch/powerpc/sysdev/xics/xics-common.c:135!
> [    0.008877] Oops: Exception in kernel mode, sig: 5 [#1]
> [    0.008908] LE SMP NR_CPUS=1024 NUMA pSeries
> [    0.008939] Modules linked in:
> [    0.008964] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G        W         5.0.13-200.fc29.ppc64le #1
> [    0.009018] NIP:  c000000001029ab8 LR: c000000001029aac CTR: c0000000018e0000
> [    0.009065] REGS: c0000007f96d7900 TRAP: 0700   Tainted: G        W          (5.0.13-200.fc29.ppc64le)
> [    0.009119] MSR:  8000000002029033 <SF,VEC,EE,ME,IR,DR,RI,LE>  CR: 28000222  XER: 20040000
> [    0.009168] CFAR: c0000000001b1e28 IRQMASK: 0
> [    0.009168] GPR00: c000000001029aac c0000007f96d7b90 c0000000015e8600 0000000000000000
> [    0.009168] GPR04: 0000000000000001 0000000000000000 0000000000000061 646f6d61696e0d0a
> [    0.009168] GPR08: 00000007fd8f0000 0000000000000001 c0000000014c44c0 c0000007f96d76cf
> [    0.009168] GPR12: 0000000000000000 c0000000018e0000 0000000000000001 0000000000000000
> [    0.009168] GPR16: 0000000000000000 0000000000000001 c0000007f96d7c08 c0000000016903d0
> [    0.009168] GPR20: c0000007fffe04e8 ffffffffffffffea c000000001620164 c00000000161fe58
> [    0.009168] GPR24: c000000000ea6c88 c0000000011151a8 00000000006000c0 c0000007f96d7c34
> [    0.009168] GPR28: 0000000000000000 c0000000014b286c c000000001115180 c00000000161dc70
> [    0.009558] NIP [c000000001029ab8] xics_smp_probe+0x38/0x98
> [    0.009590] LR [c000000001029aac] xics_smp_probe+0x2c/0x98
> [    0.009622] Call Trace:
> [    0.009639] [c0000007f96d7b90] [c000000001029aac] xics_smp_probe+0x2c/0x98 (unreliable)
> [    0.009687] [c0000007f96d7bb0] [c000000001033404] pSeries_smp_probe+0x40/0xa0
> [    0.009734] [c0000007f96d7bd0] [c0000000010212a4] smp_prepare_cpus+0x62c/0x6ec
> [    0.009782] [c0000007f96d7cf0] [c0000000010141b8] kernel_init_freeable+0x148/0x448
> [    0.009829] [c0000007f96d7db0] [c000000000010ba4] kernel_init+0x2c/0x148
> [    0.009870] [c0000007f96d7e20] [c00000000000bdd4] ret_from_kernel_thread+0x5c/0x68
> [    0.009916] Instruction dump:
> [    0.009940] 7c0802a6 60000000 7c0802a6 38800002 f8010010 f821ffe1 3c62001c e863b9a0
> [    0.009988] 4b1882d1 60000000 7c690034 5529d97e <0b090000> 3d22001c e929b998 3ce2ff8f
> 
> Look for xive=off during prom_init and don't ask for XIVE in this case. One
> exception though: if the host only supports XIVE, we still want to boot so
> we ignore xive=off.
> 
> Similarly, have the spapr XIVE init code to looking at the interrupt mode
> negociated during CAS, and ignore xive=off if the hypervisor only supports
> XIVE.
> 
> Fixes: eac1e731b59e ("powerpc/xive: guest exploitation of the XIVE interrupt controller")
> Cc: [email-masked] # v4.20
> Reported-by: Pavithra R. Prakash <[email-masked]>
> Signed-off-by: Greg Kurz <[email-masked]>
> Reviewed-by: Cédric Le Goater <[email-masked]>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/a3bf9fbdad600b1e4335dd90979f8d60

cheers