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From: =?iso-8859-1?Q?Fran=E7ois-Fr=E9d=E9ric_Ozog?= <ff-SpBG2i6TTxU@public.gmane.org>
Subject: Re: Issue when the kernel parameter intel_iommu=on is
	being	used
Date: Sun, 5 Jan 2014 18:28:47 +0100
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To: "'Sridhar S'" <sridhar.nest-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	<dev-VfR2kkLFssw@public.gmane.org>
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Hi,

To understand the issue, you may have a look at:
http://www.intel.com/content/www/us/en/intelligent-systems/intel-technolo=
gy/
vt-directed-io-spec.html

When you have no IOMMU, "physical" address space is accessed directly by
hardware, so your core works.

When VT-d is active, there is DMA/IRQ remapping hardware layer between =
the
device and the memory/cpu. If you look at =A73.4.3 of the spec, you that =
for
each device of each bus there is a context (enumerated at boot time,
leveraging BIOS/ACPI). For each device, you may have address translation
programmed so that DMA produced by hardware is actually mapped to a =
physical
address.

When you use the Linux kernel API for mapping DMA memory, Linux takes =
care
of the "details".=20

For DPDK, documentation =A75.6 Using Linux IOMMU Pass-Through to Run =
Intel=AE
DPDK with Intel=AE VT-d says that you should have iommu=3Dpt kernel =
parameter
on. Do you have it ?

FF


> -----Message d'origine-----
> De=A0: dev [mailto:dev-bounces-VfR2kkLFssw@public.gmane.org] De la part de Sridhar S
> Envoy=E9=A0: dimanche 5 janvier 2014 13:38
> =C0=A0: dev-VfR2kkLFssw@public.gmane.org
> Objet=A0: [dpdk-dev] Issue when the kernel parameter intel_iommu=3Don =
is being
> used
>=20
> Hello,
>=20
>=20
>=20
> I am using DPDK 1.5 for development of host pmd for device =93Connect =
X3=94.
>=20
>=20
>=20
> I am observing issue  while the ConnectX3 device DMA to a memory which =
is
> allocated with rte_memzone_reserve_aligned() API .
>=20
> The issue(please refer ERROR below) has been observed if the system =
runs
> with the kernel parameter =93intel_iommu=3Don=94.
>=20
>=20
>=20
> ERROR :
>=20
> dmar: DRHD: handling fault status reg 302
>=20
> dmar: DMAR:[DMA Write] Request device [01:00.0] fault addr 4f883000
>=20
> DMAR:[fault reason 01] Present bit in root entry is clear
>=20
>=20
> The reported "fault Addr" is the physical address which was returned =
by
the
> Above API.
>=20
>=20
>=20
> I don=92t see any issue with the same code when the system up with =
kernel
> parameter intel_iommu=3Doff.
>=20
>=20
>=20
>=20
> Can you share your comments on this issue?
>=20
>=20
> Thanks in advance
>=20
> Sri