Re: [PATCH 2/2] arm64: dts: juno: Enable more SMMUs

[Robin Murphy]

On 2021-07-30 15:34, Anders Roxell wrote:
> On 2021-07-30 13:17, Robin Murphy wrote:
> > On 2021-07-30 12:35, Anders Roxell wrote:
> > > From: Robin Murphy <robin.murphy@xxxxxxx>
> > >
> > > > Now that PCI inbound window restrictions are handled generically between
> > > > the of_pci resource parsing and the IOMMU layer, and described in the
> > > > Juno DT, we can finally enable the PCIe SMMU without the risk of DMA
> > > > mappings inadvertently allocating unusable addresses.
> > > >
> > > > Similarly, the relevant support for IOMMU mappings for peripheral
> > > > transfers has been hooked up in the pl330 driver for ages, so we can
> > > > happily enable the DMA SMMU without that breaking anything either.
> > > >
> > > > Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>
> > >
> > > When we build a kernel with 64k page size and run the ltp syscalls we
> > > sporadically see a kernel crash while doing a mkfs on a connected SATA
> > > drive.  This is happening every third test run on any juno-r2 device in
> > > the lab with the same kernel image (stable-rc 5.13.y, mainline and next)
> > > with gcc-11.
> >
> > Hmm, I guess 64K pages might make a difference in that we'll chew through
> > IOVA space a lot faster with small mappings...
> >
> > I'll have to try to reproduce this locally, since the interesting thing
> > would be knowing what DMA address it was trying to use that went wrong, but
> > IOMMU tracepoints and/or dma-debug are going to generate an crazy amount of
> > data to sift through and try to correlate - having done it before it's not
> > something I'd readily ask someone else to do for me :)
> >
> > On a hunch, though, does it make any difference if you remove the first
> > entry from the PCIe "dma-ranges" (the 0x2c1c0000 one)?
>
> I did this change, and run the job 7 times and could not reproduce the
> issue.

Thanks! And hold that thought; if it works then I suspect it probably is 
the best fix, but I'll double-check and write it up properly next week.

Cheers,
Robin.

> diff --git a/arch/arm64/boot/dts/arm/juno-base.dtsi b/arch/arm64/boot/dts/arm/juno-base.dtsi
> index 8e7a66943b01..d3148730e951 100644
> --- a/arch/arm64/boot/dts/arm/juno-base.dtsi
> +++ b/arch/arm64/boot/dts/arm/juno-base.dtsi
> @@ -545,8 +545,7 @@ pcie_ctlr: pcie@40000000 {
>                           <0x02000000 0x00 0x50000000 0x00 0x50000000 0x0 0x08000000>,
>                           <0x42000000 0x40 0x00000000 0x40 0x00000000 0x1 0x00000000>;
>                  /* Standard AXI Translation entries as programmed by EDK2 */
> -               dma-ranges = <0x02000000 0x0 0x2c1c0000 0x0 0x2c1c0000 0x0 0x00040000>,
> -                            <0x02000000 0x0 0x80000000 0x0 0x80000000 0x0 0x80000000>,
> +               dma-ranges = <0x02000000 0x0 0x80000000 0x0 0x80000000 0x0 0x80000000>,
>                               <0x43000000 0x8 0x00000000 0x8 0x00000000 0x2 0x00000000>;
>                  #interrupt-cells = <1>;
>                  interrupt-map-mask = <0 0 0 7>;
>
>
> Cheers,
> Anders