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Wed, 3 Dec 2025 21:45:09 GMT Received: from smtpav05.wdc07v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id ED50958069; Wed, 3 Dec 2025 21:45:08 +0000 (GMT) Received: from smtpav05.wdc07v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id AD73858053; Wed, 3 Dec 2025 21:45:05 +0000 (GMT) Received: from [9.111.80.152] (unknown [9.111.80.152]) by smtpav05.wdc07v.mail.ibm.com (Postfix) with ESMTP; Wed, 3 Dec 2025 21:45:05 +0000 (GMT) Message-ID: Subject: Re: [PATCH v5 1/2] PCI: Fix isolated PCI function probing with ARI and SR-IOV From: Niklas Schnelle To: Huacai Chen Cc: Tianrui Zhao , Bibo Mao , Bjorn Helgaas , Jan Kiszka , linux-s390 , loongarch@lists.linux.dev, Farhan Ali , Matthew Rosato , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Sven Schnelle , Christian Borntraeger , Gerd Bayer , linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org Date: Wed, 03 Dec 2025 22:45:04 +0100 In-Reply-To: References: <20251029-ari_no_bus_dev-v5-0-d9a5eab67ed0@linux.ibm.com> <20251029-ari_no_bus_dev-v5-1-d9a5eab67ed0@linux.ibm.com> <958ef380be4ea488698fab05245d631998c32a48.camel@linux.ibm.com> <8dd0f3df4b18a6c9f8b49ede7bc2ab71e40fd8f9.camel@linux.ibm.com> <7385677843a7790e01158644f63ae4dbb3353bfe.camel@linux.ibm.com> <298aaf6b2815e59d1a94efffdd0e3b002c000cea.camel@linux.ibm.com> Autocrypt: addr=schnelle@linux.ibm.com; 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charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.58.2 (3.58.2-1.fc43) 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-Spam-Details-Enc: AW1haW4tMjUxMTI5MDAwMCBTYWx0ZWRfX+NzvQYtOWsv0 lKEtpag2NIcrdLEaMnzbCBFivFzKQMan2pG6NTEPKAmW4Jds8s0dF41rCxd2YXOhu3nWY5JzeJr OhKXaVzRKoxppy8Q8ngdoI+DrObt/Esm524cflLAh4i16ahhoHrZ2yzwTavRDyy/5HkS6gLYfpJ MxkwC3IMbngcYCykJKJF3saQyp1K1D/v8cq6eyiKXD6sEb/nrgsTsQ2f25WvamJAivqIwRrw9qV tTKlO7NbbltlNq3hMvQQVI8/LKUHKUmEJZPi5fErxIzCbdBZStwiSRKxw/pesvKUs6YSKkESLjp rWUaYrLiy6zUjkEsYSzZSv+OR81UWQP3chM8rFdryliOLi6B/LEKVJfpA4d++RrZyNWlDmCAZIX Mt7jDJBtJPmgEhcipvPpCcatYwqlfA== X-Authority-Analysis: v=2.4 cv=dIerWeZb c=1 sm=1 tr=0 ts=6930af67 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=wP3pNCr1ah4A:10 a=VkNPw1HP01LnGYTKEx00:22 a=5gJIf5bccVYq2KwzBKQA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: M16xe1CiTStw0iZsDQA8qMh-U4aKzUFD X-Proofpoint-GUID: KDfZ4tdNi--A2JNzvpmoJxaHIFoQ0u7p X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-12-03_03,2025-12-03_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 lowpriorityscore=0 clxscore=1015 spamscore=0 malwarescore=0 suspectscore=0 adultscore=0 bulkscore=0 impostorscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2510240000 definitions=main-2511290000 On Mon, 2025-12-01 at 22:45 +0800, Huacai Chen wrote: >=20 --- snip --- > You said that "it feels like this is just a hack to probe an odd > topology". Yes, to some extent you are right. >=20 > 1, One of our SoC (LS2K3000) has a special device which has func1 but > without func0. To let the PCI core scan func1 we can only make > hypervisor_isolated_pci_functions() return true. > 2, In the above case, PCI_SCAN_ALL_PCIE_DEVS has no help. > 3, Though we change hypervisor_isolated_pci_functions() to resolve the > above problem, it also lets us pass isolated PCI functions to a guest > OS instance. >=20 > As a summary, for real machines commit a02fd05661d73a850 is a hack to > probe an odd device, for virtual machines it allows passing isolated > PCI functions. Ok, thanks for the answer. So let's see how we can debug this and get to a solution that works for both of us. Looking around a bit I see that your pci_loongson_map_bus() has some special handling for trying not to access non-existent devices added by your commit 2410e3301fcc ("PCI: loongson: Don't access non-existent devices"). I wonder if with this patch applied we're running into this same issue but with a devfn that was previously not tried and is not covered by your checks?=C2=A0And maybe since your root complex doesn't return 0xff for these non- existent devices we could end up trying to probe AHCI on such an empty slot misinterpreting whatever it returns as matching device/vendor? And looking at pdev_may_exist() does the "device <=3D 20" really make sense with 20 in decimal? If I pull in the negation I get "device > 19" But if it was 0x20 I'd get "device > 0x1f" which would match the maximum value of PCI_SLOT(), though then the check would be redundant since the device value already comes out of PCI_SLOT(). Could you try redoing the test with the AHCI hang but add a print of the affected bus/device/function that AHCI thinks it is probing? Then if the above theory applies we should see it trying to probe on a device that is missing in the correctly booted case and got past your existing checks. Thanks, Niklas Schnelle