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Tue, 5 Nov 2024 15:34:08 GMT Received: from smtpav03.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id DFD845803F; Tue, 5 Nov 2024 15:34:07 +0000 (GMT) Received: from smtpav03.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 41BFB58061; Tue, 5 Nov 2024 15:34:05 +0000 (GMT) Received: from [9.152.212.119] (unknown [9.152.212.119]) by smtpav03.dal12v.mail.ibm.com (Postfix) with ESMTP; Tue, 5 Nov 2024 15:34:05 +0000 (GMT) Message-ID: <8d6535b523f2aad694e5825ac3f514cff788b2bf.camel@linux.ibm.com> Subject: Re: [PATCH v2] PCI: s390: Handle ARI on bus without associated struct pci_dev From: Niklas Schnelle To: Bjorn Helgaas , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Sven Schnelle , Christian Borntraeger , Gerd Bayer Cc: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org Date: Tue, 05 Nov 2024 16:34:04 +0100 In-Reply-To: <20240918-ari_no_bus_dev-v2-1-83cfa991082f@linux.ibm.com> References: <20240918-ari_no_bus_dev-v2-1-83cfa991082f@linux.ibm.com> Autocrypt: addr=schnelle@linux.ibm.com; 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charset="UTF-8" User-Agent: Evolution 3.52.4 (3.52.4-2.fc40) X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: HyU4bCelNQgopBVc-VvxUY2AquQ01MAu X-Proofpoint-GUID: Fu_ZUpmqzRQNVAlfxDF8GIJD75wLXbMI Content-Transfer-Encoding: quoted-printable X-Proofpoint-UnRewURL: 0 URL was un-rewritten Precedence: bulk X-Mailing-List: linux-pci@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1051,Hydra:6.0.680,FMLib:17.12.62.30 definitions=2024-10-15_01,2024-10-11_01,2024-09-30_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 phishscore=0 mlxscore=0 bulkscore=0 spamscore=0 impostorscore=0 mlxlogscore=639 lowpriorityscore=0 priorityscore=1501 adultscore=0 clxscore=1011 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2409260000 definitions=main-2411050121 On Wed, 2024-09-18 at 11:04 +0200, Niklas Schnelle wrote: > On s390 PCI busses are virtualized and the downstream ports are > invisible to the OS and struct pci_bus::self is NULL. This associated > struct pci_dev is however relied upon in pci_ari_enabled() to check > whether ARI is enabled for the bus. ARI is therefor always detected as > disabled. >=20 > At the same time firmware on s390 always enables and relies upon ARI > thus causing a mismatch. Moreover with per-PCI function pass-through > there may exist busses with no function with devfn 0. For example > a SR-IOV capable device with two PFs may have separate function > dependency link chains for each of the PFs and their child VFs. In this > case the OS may only see the second PF and its child VFs on a bus > without a devfn 0 function. A situation which is also not supported by > the common pci_configure_ari() code. >=20 > Dispite simply being a mismatch this causes problems as some PCI devices > present a different SR-IOV topology depending on PCI_SRIOV_CTRL_ARI. >=20 > A similar mismatch may occur with SR-IOV when virtfn_add_bus() creates new > busses with no associated struct pci_dev. Here too pci_ari_enabled() > on these busses would return false even if ARI is actually used. >=20 > Prevent both mismatches by moving the ari_enabled flag from struct > pci_dev to struct pci_bus making it independent from struct pci_bus:: > self. Let the bus inherit the ari_enabled state from its parent bus when > there is no bridge device such that busses added by virtfn_add_bus() > match their parent. For s390 set ari_enabled when the device supports > ARI in the awareness that all PCIe ports on s390 systems are ARI > capable. >=20 > Signed-off-by: Niklas Schnelle > --- > Note: In a comment of the v1 thread I discussed an alternative idea for > a generic solution that would include the Jailhouse hypervisor via > hypervisor_isolated_pci_functions(). As Bjorn correctly pointed out this > more generic solution however lacks a way to indicate that ARI is really > enabled in the hardware. So instead for now I propose to stick with this > patch which only enables this unconditionally on s390x and SR-IOV > virtual busses where the ARI is inherited. > --- > Changes in v2: > - Rebased on v6.11 > - Link to v1: https://lore.kernel.org/r/20240730-ari_no_bus_dev-v1-1-7de1= 7676f9fe@linux.ibm.com >=20 >=20 @Bjorn, this seems to have dropped off your radar or would you like me to see if I can find a different approach? Thanks, Niklas