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<53c930df7058288776392073964a70025ca62d19.camel@linux.ibm.com> Subject: Re: [PATCH v3 3/3] iommu/s390: implement iommu passthrough via identity domain From: Niklas Schnelle To: Matthew Rosato , joro@8bytes.org, will@kernel.org, robin.murphy@arm.com, gerald.schaefer@linux.ibm.com Cc: hca@linux.ibm.com, gor@linux.ibm.com, agordeev@linux.ibm.com, svens@linux.ibm.com, borntraeger@linux.ibm.com, farman@linux.ibm.com, clegoate@redhat.com, iommu@lists.linux.dev, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org Date: Thu, 30 Jan 2025 08:43:38 +0100 In-Reply-To: <20250124201717.348736-4-mjrosato@linux.ibm.com> References: <20250124201717.348736-1-mjrosato@linux.ibm.com> <20250124201717.348736-4-mjrosato@linux.ibm.com> Autocrypt: addr=schnelle@linux.ibm.com; prefer-encrypt=mutual; keydata=mQINBGHm3M8BEAC+MIQkfoPIAKdjjk84OSQ8erd2OICj98+GdhMQpIjHXn/RJdCZLa58k /ay5x0xIHkWzx1JJOm4Lki7WEzRbYDexQEJP0xUia0U+4Yg7PJL4Dg/W4Ho28dRBROoJjgJSLSHwc 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UO2yxhPHgoW99OuZw3IRHe0+mNR67JbIpSuFWDFNjZ0nckQcU1taSEUi0euWs7i4MEkm0NsOsVhbs 4D2vMiC6kO/FqWOPmWZeAjyJw/KRUG4PaJAr5zJUx57nhKWgeTniW712n4DwCUh77D/PHY0nqBTG/ B+QQCR/FYGpTFkO4DRVfapT8njDrsWyVpP9o64VNZP42S+DuRGWfUKCMAXsM/wPzRiDEVfnZMcUR9 vwLSHeoV7MiIFC0xIrp5ES9R00t4UFgqtGc36DV71qjR+66Im0= Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.54.3 (3.54.3-1.fc41) Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: SnQ_F1zm6vnT9POTI9bQ-tzd1zNUBuoF X-Proofpoint-GUID: SnQ_F1zm6vnT9POTI9bQ-tzd1zNUBuoF X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1057,Hydra:6.0.680,FMLib:17.12.68.34 definitions=2025-01-30_03,2025-01-29_01,2024-11-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 mlxlogscore=999 phishscore=0 clxscore=1015 adultscore=0 priorityscore=1501 spamscore=0 impostorscore=0 malwarescore=0 suspectscore=0 mlxscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2411120000 definitions=main-2501300057 On Fri, 2025-01-24 at 15:17 -0500, Matthew Rosato wrote: > Enabled via the kernel command-line 'iommu.passthrough=3D1' option. >=20 > Introduce the concept of identity domains to s390-iommu, which relies on > the bus_dma_region to offset identity mappings to the start of the DMA > aperture advertized by CLP. >=20 > Signed-off-by: Matthew Rosato > --- > arch/s390/pci/pci.c | 6 ++- > drivers/iommu/s390-iommu.c | 95 +++++++++++++++++++++++++++++--------- > 2 files changed, 76 insertions(+), 25 deletions(-) >=20 > diff --git a/arch/s390/pci/pci.c b/arch/s390/pci/pci.c > index 88f72745fa59..758b23331754 100644 > --- a/arch/s390/pci/pci.c > +++ b/arch/s390/pci/pci.c > @@ -124,14 +124,16 @@ int zpci_register_ioat(struct zpci_dev *zdev, u8 dm= aas, > struct zpci_fib fib =3D {0}; > u8 cc; > =20 > - WARN_ON_ONCE(iota & 0x3fff); > fib.pba =3D base; > /* Work around off by one in ISM virt device */ > if (zdev->pft =3D=3D PCI_FUNC_TYPE_ISM && limit > base) > fib.pal =3D limit + (1 << 12); > else > fib.pal =3D limit; > - fib.iota =3D iota | ZPCI_IOTA_RTTO_FLAG; > + if (iota =3D=3D 0) > + fib.iota =3D iota; Taking another look, I think there is a small problem with the logic of passing iota =3D=3D 0 to indicate direct mapping. In zpci_hot_reset_device() we call zpci_register_ioat() with iota set to virt_to_phys(zdev->dma_table) and while zdev->dma_table is NULL for the identity domain we can't rely on virt_to_phys(NULL) =3D=3D NULL. > + else > + fib.iota =3D iota | ZPCI_IOTA_RTTO_FLAG; > fib.gd =3D zdev->gisa; > cc =3D zpci_mod_fc(req, &fib, status); > if (cc)