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Wed, 12 Feb 2025 15:23:50 +0000 (GMT) Message-ID: <52a8f09c-4a59-4439-9738-58f040fed0a5@linux.ibm.com> Date: Wed, 12 Feb 2025 10:23:50 -0500 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 2/4] s390/pci: store DMA offset in bus_dma_region To: Niklas Schnelle , 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, jgg@nvidia.com, iommu@lists.linux.dev, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, Halil Pasic References: <20250207205335.473946-1-mjrosato@linux.ibm.com> <20250207205335.473946-3-mjrosato@linux.ibm.com> <8380fe8052c9b972a8350394cb6655f6a9683d29.camel@linux.ibm.com> Content-Language: en-US From: Matthew Rosato In-Reply-To: <8380fe8052c9b972a8350394cb6655f6a9683d29.camel@linux.ibm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: g6NXWJHWIR4QEE_Sby7jnx0AU6CaX6Nn X-Proofpoint-ORIG-GUID: g6NXWJHWIR4QEE_Sby7jnx0AU6CaX6Nn 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=2025-02-12_04,2025-02-11_01,2024-11-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 malwarescore=0 mlxscore=0 lowpriorityscore=0 adultscore=0 bulkscore=0 priorityscore=1501 mlxlogscore=611 clxscore=1015 phishscore=0 impostorscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2501170000 definitions=main-2502120114 >> +static void pci_dma_range_setup(struct pci_dev *pdev) >> +{ >> + struct zpci_dev *zdev = to_zpci(pdev); >> + struct bus_dma_region *map; >> + >> + map = kzalloc(sizeof(*map), GFP_KERNEL); >> + if (!map) >> + return; >> + >> + map->cpu_start = 0; >> + map->dma_start = PAGE_ALIGN(zdev->start_dma); >> + map->size = max(PAGE_ALIGN_DOWN(zdev->end_dma + 1) - map->dma_start, 0); > > Ugh, this is my fault as I suggested it, but this max() doesn't work > here. The zdev->end_dma is unsigned and so is map->dma_start so if the > former is smaller underflow will occur and the max() won't save us. > It's largely a theoretical issue since zdev->end_dma + 1 should always > be larger than zdev->start_dma, but now the max() looks like we thought > of that, but then it doesn't work. > > If we handle it maybe just go with: > > aligned_end = PAGE_ALIGN_DOWN(zdev->end_dma + 1); > if (aligned_end >= map->dma_start) > map->size = aligned_end - map->dma_start; > else > map->size = 0; > Given that it's not really something that's supposed to happen, would it make sense then to add a WARN_ON_ONCE(map->size == 0); At the end of this?