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Tue, 30 Sep 2025 17:04:25 +0000 (GMT) Message-ID: <1f5abbae-7a7d-402d-ac6e-029cdc3b0d63@linux.ibm.com> Date: Tue, 30 Sep 2025 10:04:25 -0700 Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 02/10] PCI: Add additional checks for flr reset To: Benjamin Block Cc: linux-s390@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, alex.williamson@redhat.com, helgaas@kernel.org, clg@redhat.com, schnelle@linux.ibm.com, mjrosato@linux.ibm.com References: <20250924171628.826-1-alifm@linux.ibm.com> <20250924171628.826-3-alifm@linux.ibm.com> <20250930100321.GB15786@p1gen4-pw042f0m.boeblingen.de.ibm.com> Content-Language: en-US From: Farhan Ali In-Reply-To: <20250930100321.GB15786@p1gen4-pw042f0m.boeblingen.de.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=T7WBjvKQ c=1 sm=1 tr=0 ts=68dc0d9c cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=yJojWOMRYYMA:10 a=BMGjUjUgpuDZBGNCpE8A:9 a=QEXdDO2ut3YA:10 a=cPQSjfK2_nFv0Q5t_7PE:22 X-Proofpoint-GUID: PQUxSMRTqZxFM1SYDVuw5HCVqKk4fY3_ X-Proofpoint-ORIG-GUID: PQUxSMRTqZxFM1SYDVuw5HCVqKk4fY3_ X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwOTI3MDAyNSBTYWx0ZWRfX28mtSnEoDnxl KxFCtQ476SvG3rWv5OYoACfPQnKSIsfeesLQE+GhAvPEYCGnanMnT6ABTjG4cMzIxjVpOjF1fV+ 8s2evQfOFS5PB0JuxofJ8lG9K29XWhhQMd/SEyiQKIemwlhUgLscNPhCprNXC6eadRac1lse/9w JOAyq02QFx7mCJLt7hKR7bvrQGCPQqDN1Lxpi5DnzA3gQWvhgLU8bmSnQOysQM9JcnjahyYzx5u sPvC1ChWZ6gxJSIPQfSdNVVVdQSddlDCblA+54qytIxNNCSlSTJPY2UDZYAknHb5FzV4BVJQQM0 THiQ3BPpu2ntAi1El7Y0O+tHd/OZ1ZJWxKPouKEcCpCLwdOUiJsz1Rgni2T/ggLCq7edjIGfAnT bh0K0MsdvY3UcQpXNQ7AqCskNP5kGA== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1117,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-09-30_03,2025-09-29_04,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 clxscore=1015 spamscore=0 suspectscore=0 priorityscore=1501 bulkscore=0 adultscore=0 lowpriorityscore=0 malwarescore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2509150000 definitions=main-2509270025 On 9/30/2025 3:03 AM, Benjamin Block wrote: > On Wed, Sep 24, 2025 at 10:16:20AM -0700, Farhan Ali wrote: >> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c >> index a3d93d1baee7..327fefc6a1eb 100644 >> --- a/drivers/pci/pci.c >> +++ b/drivers/pci/pci.c >> @@ -4576,12 +4576,19 @@ EXPORT_SYMBOL_GPL(pcie_flr); >> */ >> int pcie_reset_flr(struct pci_dev *dev, bool probe) >> { >> + u32 reg; >> + >> if (dev->dev_flags & PCI_DEV_FLAGS_NO_FLR_RESET) >> return -ENOTTY; >> >> if (!(dev->devcap & PCI_EXP_DEVCAP_FLR)) >> return -ENOTTY; >> >> + if (pcie_capability_read_dword(dev, PCI_EXP_DEVCAP, ®)) { >> + pci_warn(dev, "Device unable to do an FLR\n"); >> + return -ENOTTY; >> + } > Just thinking out loud, not sure whether it make sense, but since you already > read an up-to-date value from the config space, would it make sense to > pull the check above `dev->devcap & PCI_EXP_DEVCAP_FLR` below this read, and > check on the just read `reg`? My thinking was we could exit early if the device never had FLR capability (and so was not cached in devcap). This way we avoid an extra PCI read. > > Also wondering whether it makes sense to stable-tag this? We've recently seen > "unpleasant" recovery attempts that look like this in the kernel logs: > > [ 663.330053] vfio-pci 0007:00:00.1: timed out waiting for pending transaction; performing function level reset anyway > [ 664.730051] vfio-pci 0007:00:00.1: not ready 1023ms after FLR; waiting > [ 665.830023] vfio-pci 0007:00:00.1: not ready 2047ms after FLR; waiting > [ 667.910023] vfio-pci 0007:00:00.1: not ready 4095ms after FLR; waiting > [ 672.070022] vfio-pci 0007:00:00.1: not ready 8191ms after FLR; waiting > [ 680.550025] vfio-pci 0007:00:00.1: not ready 16383ms after FLR; waiting > [ 697.190023] vfio-pci 0007:00:00.1: not ready 32767ms after FLR; waiting > [ 730.470021] vfio-pci 0007:00:00.1: not ready 65535ms after FLR; giving up > > The VF here was already dead in the water at that point, so I suspect > `pci_read_config_dword()` might have failed, and so this check would have > failed, and we wouldn't have "wasted" the minute waiting for a FLR that was > never going to happen anyway. I think maybe we could? I don't think this patch fixes anything that's "broken" but rather improves the behavior to escalate to other reset method if the device is already in a bad state. I will cc stable. Thanks Farhan