Re: [PATCH] powerpc/powernv/npu: Fix oops in pnv_try_setup_npu_table_group()

[Greg KH <greg@kroah.com>]

On Thu, Jan 10, 2019 at 01:58:31PM +0100, Frederic Barrat wrote:
> 
> 
> Le 10/01/2019 à 13:25, Michael Ellerman a écrit :
> > Greg Kurz <groug@kaod.org> writes:
> > > On Wed, 9 Jan 2019 17:45:53 +0100
> > > Frederic Barrat <fbarrat@linux.ibm.com> wrote:
> > > 
> > > > Le 09/01/2019 à 17:25, Greg Kurz a écrit :
> > > > > On Wed,  9 Jan 2019 16:13:42 +0100
> > > > > Frederic Barrat <fbarrat@linux.ibm.com> wrote:
> > > > > > 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=2048 NUMA PowerNV
> > > > > > Modules linked in:
> > > > > > CPU: 5 PID: 1 Comm: swapper/4 Not tainted 5.0.0-rc1-fxb-00001-g3bd6e94bec12
> > > > > > NIP:  c0000000000aa38c LR: c0000000000a6608 CTR: c000000000097480
> > > > > > REGS: c000000005783700 TRAP: 0300   Not tainted  (5.0.0-rc1-fxb-00001-g3bd6
> > > > > > MSR:  9000000002009033 <SF,HV,VEC,EE,ME,IR,DR,RI,LE>  CR: 28000228  XER: 20
> > > > > > CFAR: c0000000000a6604 DAR: 0000000000000028 DSISR: 00080000 IRQMASK: 0
> > > > > > GPR00: c0000000000a6608 c000000005783990 c000000001036100 c0000007bf761860
> > > > > > GPR04: 0000000000000000 c000000005783834 0000000000000000 0000000000000000
> > > > > > GPR08: 69626d2c6e707500 0000000000000000 0000000000000000 9000000002001003
> > > > > > GPR12: 0000000000000000 c0000007bfff8300 c000000000010450 0000000000000000
> > > > > > GPR16: c000000000ced938 0000000000000100 c000000000ced948 00000000000a0000
> > > > > > GPR20: 00000000000bfffe c000000000ced9a8 0000000000000200 c000000000ced978
> > > > > > GPR24: 00000000006080c0 c000000716d09828 c00000002e6fd000 0000000000000000
> > > > > > GPR28: c0000007bf4aff68 c0000007bf8d0080 c000000000f23938 c0000007bf761860
> > > > > > 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/0x468
> > > > > > [c000000005783db0] [c000000000010474] kernel_init+0x2c/0x148
> > > > > > [c000000005783e20] [c00000000000b794] ret_from_kernel_thread+0x5c/0x68
> > > > > > 
> > > > > > 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 opencapi,
> > > > > > as the device sends real addresses directly (admittedly, the
> > > > > > virtualization story is yet to be written). So let's fix it by
> > > > > 
> > > > > 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.
> > > > > > skipping the IOMMU group setup for opencapi PHBs.
> > > > > > 
> > > > > > Fixes: 0bd971676e68 ("powerpc/powernv/npu: Add compound IOMMU groups")
> > > > > > Signed-off-by: Frederic Barrat <fbarrat@linux.ibm.com>
> > > > > > ---
> > > > > 
> > > > > Reviewed-by: Greg Kurz <groug@kaod.org>
> > > > > 
> > > > > and
> > > > > 
> > > > > Cc: stable@vger.kernel.org      # v4.20
> > > > 
> > > > Thanks for the review! But why did you add stable? that problem is only
> > > > seen on 5.0-rc1, isn't it?
> > > 
> > > Based on the fact that 0bd971676e68 was committed in 4.20... but I haven't
> > > tested :)
> > 
> > It was committed to a branch based off 4.20-rc2, but it wasn't merged
> > into the 4.20 release.
> > 
> >    $ git describe --match "v[0-9]*" --contains 0bd971676e68
> >    v5.0-rc1~137^2~15
> > 
> > So it doesn't need to go to stable.
> 
> Which makes me wonder if Greg (KH) was really talking about that original
> patch and whether something worthwhile was dropped from stable by mistake?

Totally different thread, sorry for the noise, my fault...

greg k-h