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Date: Thu, 10 Jan 2019 13:31:25 +0100
From: Greg Kurz <groug@kaod.org>
To: Michael Ellerman <mpe@ellerman.id.au>
Subject: Re: [PATCH] powerpc/powernv/npu: Fix oops in
 pnv_try_setup_npu_table_group()
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On Thu, 10 Jan 2019 23:25:11 +1100
Michael Ellerman <mpe@ellerman.id.au> wrote:

> Greg Kurz <groug@kaod.org> writes:
> > On Wed, 9 Jan 2019 17:45:53 +0100
> > Frederic Barrat <fbarrat@linux.ibm.com> wrote:
> > =20
> >> Le 09/01/2019 =C3=A0 17:25, Greg Kurz a =C3=A9crit=C2=A0: =20
> >> > On Wed,  9 Jan 2019 16:13:42 +0100
> >> > Frederic Barrat <fbarrat@linux.ibm.com> wrote:
> >> >    =20
> >> >> With a recent change around IOMMU group, a system with an opencapi
> >> >> adapter is no longer booting and we get a kernel oops:
> >> >>
> >> >> BUG: Kernel NULL pointer dereference at 0x00000028
> >> >> Faulting instruction address: 0xc0000000000aa38c
> >> >> Oops: Kernel access of bad area, sig: 7 [#1]
> >> >> LE SMP NR_CPUS=3D2048 NUMA PowerNV
> >> >> Modules linked in:
> >> >> CPU: 5 PID: 1 Comm: swapper/4 Not tainted 5.0.0-rc1-fxb-00001-g3bd6=
e94bec12
> >> >> NIP:  c0000000000aa38c LR: c0000000000a6608 CTR: c000000000097480
> >> >> REGS: c000000005783700 TRAP: 0300   Not tainted  (5.0.0-rc1-fxb-000=
01-g3bd6
> >> >> MSR:  9000000002009033 <SF,HV,VEC,EE,ME,IR,DR,RI,LE>  CR: 28000228 =
 XER: 20
> >> >> CFAR: c0000000000a6604 DAR: 0000000000000028 DSISR: 00080000 IRQMAS=
K: 0
> >> >> GPR00: c0000000000a6608 c000000005783990 c000000001036100 c0000007b=
f761860
> >> >> GPR04: 0000000000000000 c000000005783834 0000000000000000 000000000=
0000000
> >> >> GPR08: 69626d2c6e707500 0000000000000000 0000000000000000 900000000=
2001003
> >> >> GPR12: 0000000000000000 c0000007bfff8300 c000000000010450 000000000=
0000000
> >> >> GPR16: c000000000ced938 0000000000000100 c000000000ced948 000000000=
00a0000
> >> >> GPR20: 00000000000bfffe c000000000ced9a8 0000000000000200 c00000000=
0ced978
> >> >> GPR24: 00000000006080c0 c000000716d09828 c00000002e6fd000 000000000=
0000000
> >> >> GPR28: c0000007bf4aff68 c0000007bf8d0080 c000000000f23938 c0000007b=
f761860
> >> >> NIP [c0000000000aa38c] pnv_try_setup_npu_table_group+0x1c/0x1a0
> >> >> LR [c0000000000a6608] pnv_pci_ioda_fixup+0x1f8/0x660
> >> >> Call Trace:
> >> >> [c000000005783990] [c0000000000aa3d0] pnv_try_setup_npu_table_group=
+0x60/0x
> >> >> [c0000000057839d0] [c0000000000a661c] pnv_pci_ioda_fixup+0x20c/0x660
> >> >> [c000000005783ab0] [c000000000e1d4c0] pcibios_resource_survey+0x2c8=
/0x31c
> >> >> [c000000005783b90] [c000000000e1caf4] pcibios_init+0xb0/0xe4
> >> >> [c000000005783c10] [c000000000010054] do_one_initcall+0x64/0x264
> >> >> [c000000005783ce0] [c000000000e1132c] kernel_init_freeable+0x36c/0x=
468
> >> >> [c000000005783db0] [c000000000010474] kernel_init+0x2c/0x148
> >> >> [c000000005783e20] [c00000000000b794] ret_from_kernel_thread+0x5c/0=
x68
> >> >>
> >> >> An opencapi device is using a device PE, so the current code breaks
> >> >> because pe->pbus is not defined.
> >> >>
> >> >> More generally, there's no need to define an IOMMU group for openca=
pi,
> >> >> as the device sends real addresses directly (admittedly, the
> >> >> virtualization story is yet to be written). So let's fix it by   =20
> >> >=20
> >> > Current plan is to go for mediated VFIO. The real HW stays under the=
 control
> >> > of the host ocxl driver, and we still don't need an IOMMU group.
> >> >    =20
> >> >> skipping the IOMMU group setup for opencapi PHBs.
> >> >>
> >> >> Fixes: 0bd971676e68 ("powerpc/powernv/npu: Add compound IOMMU group=
s")
> >> >> Signed-off-by: Frederic Barrat <fbarrat@linux.ibm.com>
> >> >> ---   =20
> >> >=20
> >> > Reviewed-by: Greg Kurz <groug@kaod.org>
> >> >=20
> >> > and
> >> >=20
> >> > Cc: stable@vger.kernel.org      # v4.20   =20
> >>=20
> >> Thanks for the review! But why did you add stable? that problem is onl=
y=20
> >> seen on 5.0-rc1, isn't it? =20
> >
> > Based on the fact that 0bd971676e68 was committed in 4.20... but I have=
n't
> > tested :) =20
>=20
> It was committed to a branch based off 4.20-rc2, but it wasn't merged
> into the 4.20 release.
>=20
>   $ git describe --match "v[0-9]*" --contains 0bd971676e68
>   v5.0-rc1~137^2~15
>=20
> So it doesn't need to go to stable.
>=20

Yeah I realized that afterwards, sorry for the noise and Happy New Year :)

> cheers