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

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Message-ID: <8b358507-dbdf-b05b-c1da-2ec9903a2912@arm.com>
Date:   Fri, 30 Jul 2021 15:44:07 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Anders Roxell <anders.roxell@...aro.org>
Cc:     sudeep.holla@....com, lorenzo.pieralisi@....com,
        liviu.dudau@....com, linux-arm-kernel@...ts.infradead.org,
        stable@...r.kernel.org, linux-kernel@...r.kernel.org,
        gregkh@...uxfoundation.org, sashal@...nel.org, arnd@...db.de,
        lkft-triage@...ts.linaro.org,
        Linux Kernel Functional Testing <lkft@...aro.org>
Subject: Re: [PATCH 2/2] arm64: dts: juno: Enable more SMMUs

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@....com>
>>>
>>>> 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@....com>
>>>
>>> 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@...00000 {
>                           <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
>