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Wed, 27 May 2026 10:13:31 -0700 (PDT) X-Received: by 2002:a05:7022:913:b0:135:e814:d03f with SMTP id a92af1059eb24-1365fc7d7e9mr8777489c88.36.1779902010729; Wed, 27 May 2026 10:13:30 -0700 (PDT) Received: from [10.0.40.30] ([51.52.155.79]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-136b3706ad6sm9223289c88.13.2026.05.27.10.13.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 27 May 2026 10:13:30 -0700 (PDT) Message-ID: <1f1b9967-7182-401c-ac30-373b73216e81@meta.com> Date: Wed, 27 May 2026 18:13:25 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/9] PCI/P2PDMA: Add CONFIG_PCI_P2PDMA_CORE Content-Language: en-GB To: Logan Gunthorpe , Alex Williamson , Leon Romanovsky , Jason Gunthorpe , Alex Mastro , =?UTF-8?Q?Christian_K=C3=B6nig?= , Bjorn Helgaas Cc: Mahmoud Adam , David Matlack , =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= , Sumit Semwal , Kevin Tian , Ankit Agrawal , Pranjal Shrivastava , Alistair Popple , Vivek Kasireddy , linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, kvm@vger.kernel.org, linux-pci@vger.kernel.org References: <20260527102319.100128-1-mattev@meta.com> <20260527102319.100128-2-mattev@meta.com> <843e8525-5927-45b5-a3e2-a5ec16234398@deltatee.com> From: Matt Evans In-Reply-To: <843e8525-5927-45b5-a3e2-a5ec16234398@deltatee.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Authority-Analysis: v=2.4 cv=H8zrBeYi c=1 sm=1 tr=0 ts=6a17263c cx=c_pps a=PfFC4Oe2JQzmKTvty2cRDw==:117 a=2UbFsIa4v//lIgRL4kGwwA==:17 a=IkcTkHD0fZMA:10 a=NGcC8JguVDcA:10 a=VkNPw1HP01LnGYTKEx00:22 a=7x6HtfJdh03M6CCDgxCd:22 a=jCddH8ec0KUNCymVuxII:22 a=VabnemYjAAAA:8 a=gXLdhW2jAAAA:8 a=1nsJja_hzN5yKYYIz30A:9 a=QEXdDO2ut3YA:10 a=6Ab_bkdmUrQuMsNx7PHu:22 a=gKebqoRLp9LExxC7YDUY:22 a=Dn9eIPSr_RzuO0KTJioD:22 X-Proofpoint-GUID: w5YJubiPl3ddO9c5SawN9DT-0EcffJe6 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNTI3MDE3MiBTYWx0ZWRfX8AK93th8eMRY WLmAKU3jA87zVcvP9iBh+3tXvxOfvutkIDO59D4bR/A0WlzwM158S3NKgmjH9sbM4MBjBuBn2Mq bGu3o6IuWU/soCzSZy4HSgorPFndLE6ljPj8X2uwvKMhSwE/fp8HZqayymYHqltoXJvBOP6OHcv vQQH+jt2J/CfBmOdTXP/wZb9laQgRIcAuz0yewl29NG76T8u7Dl8St0Hwd86Jn2vylVeQp6GFu5 Fav/OtxUDGHQP+HeiewjiKKcXYppy9ArgfdcEhXnFj3PjmLO7O3sM1oWWRb01QcHFtcuYTXAuMO lNPcd0LaKLNvRz6CvjKLtdHTgkm4ZeCx+pjJQxmQE3q079ZADiZOguVMIlNiaygN9YBbyh8qOTv jaLeOvVfBmqvN09T2s1gHAYncjBwubFBas9e+x43C+rQ2VeOW8dohTnbJe5wrkYEa/GNcId8Hj6 AMGpjDWU/ttxlQ3IFjg== X-Proofpoint-ORIG-GUID: w5YJubiPl3ddO9c5SawN9DT-0EcffJe6 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.125,FMLib:17.12.100.49 definitions=2026-05-27_03,2026-05-26_03,2025-10-01_01 Hi Logan, On 27/05/2026 17:07, Logan Gunthorpe wrote: > > On 2026-05-27 04:23, Matt Evans wrote: >> The P2PDMA code currently provides two features under the same >> CONFIG_PCI_P2PDMA option: >> >> 1. Locate providers via pcim_p2pdma_provider() >> 2. Manage actual P2P DMA >> >> Other code (such as vfio-pci) depends on 1, without having a hard >> dependency on 2. >> >> A future commit expands the use of DMABUF in vfio-pci for non-P2P >> scenarios, relying on pcim_p2pdma_provider() always being present. If >> that depended on CONFIG_PCI_P2PDMA, it would make vfio-pci only >> available if CONFIG_ZONE_DEVICE is present (e.g. 64-bit systems), even >> when P2P is not needed. >> >> To resolve this, introduce CONFIG_PCI_P2PDMA_CORE which contains the >> basic provider functionality to make it available even if the >> CONFIG_PCI_P2PDMA feature is disabled or unavailable due to >> !CONFIG_ZONE_DEVICE. Users such as vfio-pci can enable their own P2P >> features based off the original CONFIG_PCI_P2PDMA (available when >> CONFIG_ZONE_DEVICE is set). >> >> Signed-off-by: Matt Evans > > Largely this looks good to me. I have one minor nit below that you can > apply or not. Either way, feel free to add: > > Reviewed-by: Logan Gunthorpe > > >> static void pci_p2pdma_release(void *data) >> { >> struct pci_dev *pdev = data; >> @@ -241,11 +251,13 @@ static void pci_p2pdma_release(void *data) >> synchronize_rcu(); >> xa_destroy(&p2pdma->map_types); >> >> +#ifdef CONFIG_PCI_P2PDMA >> if (!p2pdma->pool) >> return; >> >> gen_pool_destroy(p2pdma->pool); >> sysfs_remove_group(&pdev->dev.kobj, &p2pmem_group); >> +#endif >> } > > I'm personally not a fan of adding #ifdefs inside functions like this. > This instance is small and easy to understand, but it can quickly become > a bit of a mess if we start adding more features. I probably would have > created a pci_p2pdma_release_pool() helper which does the inverse of > pci_p2pdma_setup_pool(), it would be called in pci_p2pdma_release() and > an empty implementation would be provided in the case where > CONFIG_PCI_P2PDMA is not set. That's cleaner, I'll do that. Thanks for the review. Matt