Re: [RESEND PATCH 0/3] Allow custom PCI resource alignment on pseries

[Shawn Anastasio]

On 5/27/19 11:01 PM, Oliver wrote:
> On Tue, May 28, 2019 at 8:56 AM Shawn Anastasio <shawn@xxxxxxxxxx> wrote:
> > Hello all,
> >
> > This patch set implements support for user-specified PCI resource
> > alignment on the pseries platform for hotplugged PCI devices.
> > Currently on pseries, PCI resource alignments specified with the
> > pci=resource_alignment commandline argument are ignored, since
> > the firmware is in charge of managing the PCI resources. In the
> > case of hotplugged devices, though, the kernel is in charge of
> > configuring the resources and should obey alignment requirements.
>
> Are you using hotplug to work around SLOF (the OF we use under qemu)
> not aligning BARs to 64K? It looks like there is a commit in SLOF to
> fix that (https://git.qemu.org/?p=SLOF.git;a=commit;f=board-qemu/slof/pci-phb.fs;h=1903174472f8800caf50c959b304501b4c01153c).

No, my application actually requires PCI hotplug at run-time.

> > The current behavior of ignoring the alignment for hotplugged devices
> > results in sub-page BARs landing between page boundaries and
> > becoming un-mappable from userspace via the VFIO framework.
> > This issue was observed on a pseries KVM guest with hotplugged
> > ivshmem devices.
>
> > With these changes, users can specify an appropriate
> > pci=resource_alignment argument on boot for devices they wish to use
> > with VFIO.
> >
> > In the future, this could be extended to provide page-aligned
> > resources by default for hotplugged devices, similar to what is done
> > on powernv by commit 382746376993 ("powerpc/powernv: Override
> > pcibios_default_alignment() to force PCI devices to be page aligned").
>
> Can we make aligning the BARs to PAGE_SIZE the default behaviour? The
> BAR assignment process is complex enough as-is so I'd rather we didn't
> add another platform hack into the mix.

Absolutely. This will still require the existing changes so that the 
custom alignment isn't flat-out ignored on pseries, but I can set
it to default to PAGE_SIZE as well, similar to how it's done on PowerNV.
I've just pushed a v3 to fix a typo and I'll incorporate this change
in v4.

> > Feedback is appreciated.
> >
> > Thanks,
> > Shawn
> >
> > Shawn Anastasio (3):
> >    PCI: Introduce pcibios_ignore_alignment_request
> >    powerpc/64: Enable pcibios_after_init hook on ppc64
> >    powerpc/pseries: Allow user-specified PCI resource alignment after
> >      init
> >
> >   arch/powerpc/include/asm/machdep.h     |  6 ++++--
> >   arch/powerpc/kernel/pci-common.c       |  9 +++++++++
> >   arch/powerpc/kernel/pci_64.c           |  4 ++++
> >   arch/powerpc/platforms/pseries/setup.c | 22 ++++++++++++++++++++++
> >   drivers/pci/pci.c                      |  9 +++++++--
> >   5 files changed, 46 insertions(+), 4 deletions(-)
> >
> > --
> > 2.20.1