RE: [PATCH] scsi: pm8001: Fix phys_to_virt() usage on dma_addr_t

Ajish.Koshy
2021-12-07T10:36:26Z

Hi John,

Well I could see this kernel panic [ 126.843958] RIP: 0010:pm80xx_chip_smp_req+0x1d6/0x2e0 [pm80xx] with respect to existing driver on my current system x86 64bit after enabling the following 2 kernel boot arguments:
-intel_iommu=on
-iommu.passthrough=0

Post application of this patch, now not observing the kernel panic and device discovery happens smoothly.

Thanks,
Ajish

-----Original Message-----
From: Niklas Cassel <Niklas.Cassel@wdc.com>
Sent: Monday, December 6, 2021 06:54 PM
To: John Garry <john.garry@huawei.com>
Cc: Ajish Koshy - I30923 <Ajish.Koshy@microchip.com>; jinpu.wang@cloud.ionos.com; jejb@linux.ibm.com; martin.petersen@oracle.com; Viswas G - I30667 <Viswas.G@microchip.com>; linux-scsi@vger.kernel.org; linux-kernel@vger.kernel.org; Damien Le Moal <damien.lemoal@opensource.wdc.com>
Subject: Re: [PATCH] scsi: pm8001: Fix phys_to_virt() usage on dma_addr_t

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On Mon, Dec 06, 2021 at 09:42:23AM +0000, John Garry wrote:
> On 29/11/2021 10:46, Ajish.Koshy@microchip.com wrote:
> > Thanks John for the update. Based on the given issue,
> > we never tested on arm server.
> >
> > Further arm testing will depend on the availability of
> > the server.
> >
> > Meanwhile will do further test on x86 and update
> > on the observations.
>
> Have you tested on x86 with the IOMMU enabled? From my limited experience,
> out of the box the IOMMU is disabled in the BIOS on x86 machines - that is a
> very general statement. But this is not just an issue specific to arm64.

My limited experience tells me the opposite, that modern x64 servers
have IOMMU enabled by default:

E.g.:
https://www.dell.com/support/manuals/en-uk/poweredge-r7515/r7515_bios_pub/processor-settings?guid=guid-ec36d324-4f45-4bc1-bb51-de2db7cc5cd9&lang=en-us
https://support.hpe.com/hpesc/public/docDisplay?docId=a00025662en_us&docLocale=en_US

This driver not working properly on a system with an IOMMU just tells
us that the number of mainline users of this driver is very low :/

Kind regards,
Niklas